Quelle nsFrameLoader.cpp Sprache: C

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
* Class for managing loading of a subframe (creation of the docshell,
* handling of loads in it, recursion-checking).
*/

#include "nsFrameLoader.h"

#include "base/basictypes.h"

#include "prenv.h"

#include "nsDocShell.h"
#include "nsIContentInlines.h"
#include "nsIDocumentViewer.h"
#include "nsIPrintSettings.h"
#include "nsIPrintSettingsService.h"
#include "mozilla/dom/Document.h"
#include "nsPIDOMWindow.h"
#include "nsIWebNavigation.h"
#include "nsIWebProgress.h"
#include "nsIDocShell.h"
#include "nsIDocShellTreeOwner.h"
#include "nsDocShellLoadState.h"
#include "nsIBaseWindow.h"
#include "nsIBrowser.h"
#include "nsContentUtils.h"
#include "nsUnicharUtils.h"
#include "nsIScriptGlobalObject.h"
#include "nsIScriptSecurityManager.h"
#include "nsFrameLoaderOwner.h"
#include "nsIFrame.h"
#include "nsSubDocumentFrame.h"
#include "nsError.h"
#include "nsIAppWindow.h"
#include "nsIScriptError.h"
#include "nsGlobalWindowInner.h"
#include "nsGlobalWindowOuter.h"
#include "nsHTMLDocument.h"
#include "nsPIWindowRoot.h"
#include "nsLayoutUtils.h"
#include "nsView.h"
#include "nsViewManager.h"
#include "nsBaseWidget.h"
#include "nsQueryObject.h"
#include "ReferrerInfo.h"
#include "nsIOpenWindowInfo.h"
#include "nsISHistory.h"
#include "nsIURI.h"
#include "nsIXULRuntime.h"
#include "nsNetUtil.h"
#include "nsFocusManager.h"
#include "nsIINIParser.h"
#include "nsAppRunner.h"
#include "nsDirectoryService.h"
#include "nsDirectoryServiceDefs.h"

#include "nsGkAtoms.h"
#include "nsNameSpaceManager.h"

#include "nsThreadUtils.h"

#include "InProcessBrowserChildMessageManager.h"

#include "ContentParent.h"
#include "BrowserParent.h"
#include "mozilla/AsyncEventDispatcher.h"
#include "mozilla/BasePrincipal.h"
#include "mozilla/ExpandedPrincipal.h"
#include "mozilla/FlushType.h"
#include "mozilla/HTMLEditor.h"
#include "mozilla/NullPrincipal.h"
#include "mozilla/Preferences.h"
#include "mozilla/PresShell.h"
#include "mozilla/PresShellInlines.h"
#include "mozilla/ProcessPriorityManager.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/ScrollContainerFrame.h"
#include "mozilla/StaticPrefs_fission.h"
#include "mozilla/Unused.h"
#include "mozilla/dom/BrowsingContext.h"
#include "mozilla/dom/ChromeMessageSender.h"
#include "mozilla/dom/Element.h"
#include "mozilla/dom/FrameCrashedEvent.h"
#include "mozilla/dom/FrameLoaderBinding.h"
#include "mozilla/dom/InProcessChild.h"
#include "mozilla/dom/MozFrameLoaderOwnerBinding.h"
#include "mozilla/dom/PBrowser.h"
#include "mozilla/dom/SessionHistoryEntry.h"
#include "mozilla/dom/SessionStoreChild.h"
#include "mozilla/dom/SessionStoreParent.h"
#include "mozilla/dom/SessionStoreUtils.h"
#include "mozilla/dom/WindowGlobalParent.h"
#include "mozilla/dom/XULFrameElement.h"
#include "mozilla/gfx/CrossProcessPaint.h"
#include "mozilla/ProfilerLabels.h"
#include "nsGenericHTMLFrameElement.h"

#include "jsapi.h"
#include "mozilla/dom/HTMLIFrameElement.h"
#include "nsSandboxFlags.h"
#include "mozilla/layers/CompositorBridgeChild.h"
#include "mozilla/dom/CustomEvent.h"

#include "mozilla/dom/ipc/StructuredCloneData.h"
#include "mozilla/WebBrowserPersistLocalDocument.h"
#include "mozilla/dom/Promise.h"
#include "mozilla/dom/PromiseNativeHandler.h"
#include "mozilla/dom/ChildSHistory.h"
#include "mozilla/dom/CanonicalBrowsingContext.h"
#include "mozilla/dom/ContentChild.h"
#include "mozilla/dom/ContentProcessManager.h"
#include "mozilla/dom/BrowserBridgeChild.h"
#include "mozilla/dom/BrowserHost.h"
#include "mozilla/dom/BrowserBridgeHost.h"
#include "mozilla/dom/BrowsingContextGroup.h"

#include "mozilla/dom/SessionStorageManager.h"
#include "mozilla/ipc/BackgroundChild.h"
#include "mozilla/ipc/PBackgroundChild.h"
#include "mozilla/dom/PBackgroundSessionStorageCache.h"
#include "mozilla/ipc/BackgroundUtils.h"

#include "mozilla/dom/HTMLBodyElement.h"

#include "mozilla/ContentPrincipal.h"

#include "buildid_section.h"
#include "mozilla/toolkit/library/buildid_reader_ffi.h"
#include "nsXPCOMPrivate.h"  // for XUL_DLL

#include "nsXULPopupManager.h"

#ifdef NS_PRINTING
#  include "nsIWebBrowserPrint.h"
#endif

#if defined(MOZ_TELEMETRY_REPORTING)
#  include "mozilla/glean/DomMetrics.h"
#endif  // defined(MOZ_TELEMETRY_REPORTING)

using namespace mozilla;
using namespace mozilla::hal;
using namespace mozilla::dom;
using namespace mozilla::dom::ipc;
using namespace mozilla::ipc;
using namespace mozilla::layers;
using namespace mozilla::layout;
using ViewID = ScrollableLayerGuid::ViewID;

using PrintPreviewResolver = std::function<void(const PrintPreviewResultInfo&)>;

// Bug 8065: Limit content frame depth to some reasonable level. This
// does not count chrome frames when determining depth, nor does it
// prevent chrome recursion.  Number is fairly arbitrary, but meant to
// keep number of shells to a reasonable number on accidental recursion with a
// small (but not 1) branching factor.  With large branching factors the number
// of shells can rapidly become huge and run us out of memory.  To solve that,
// we'd need to re-institute a fixed version of bug 98158.
#define MAX_DEPTH_CONTENT_FRAMES 10

NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(nsFrameLoader, mPendingBrowsingContext,
                                      mMessageManager, mChildMessageManager,
                                      mRemoteBrowser, mSessionStoreChild)
NS_IMPL_CYCLE_COLLECTING_ADDREF(nsFrameLoader)
NS_IMPL_CYCLE_COLLECTING_RELEASE(nsFrameLoader)

NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsFrameLoader)
  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
  NS_INTERFACE_MAP_ENTRY_CONCRETE(nsFrameLoader)
  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
  NS_INTERFACE_MAP_ENTRY(nsISupports)
NS_INTERFACE_MAP_END

nsFrameLoader::nsFrameLoader(Element* aOwner, BrowsingContext* aBrowsingContext,
                             bool aIsRemoteFrame, bool aNetworkCreated)
    : mPendingBrowsingContext(aBrowsingContext),
      mOwnerContent(aOwner),
      mDetachedSubdocFrame(nullptr),
      mPendingSwitchID(0),
      mChildID(0),
      mRemoteType(NOT_REMOTE_TYPE),
      mInitialized(false),
      mDepthTooGreat(false),
      mIsTopLevelContent(false),
      mDestroyCalled(false),
      mNeedsAsyncDestroy(false),
      mInSwap(false),
      mInShow(false),
      mHideCalled(false),
      mNetworkCreated(aNetworkCreated),
      mLoadingOriginalSrc(false),
      mShouldCheckForRecursion(false),
      mRemoteBrowserShown(false),
      mRemoteBrowserSized(false),
      mIsRemoteFrame(aIsRemoteFrame),
      mWillChangeProcess(false),
      mObservingOwnerContent(false),
      mHadDetachedFrame(false),
      mTabProcessCrashFired(false) {
  nsCOMPtr<nsFrameLoaderOwner> owner = do_QueryInterface(aOwner);
  owner->AttachFrameLoader(this);
}

nsFrameLoader::~nsFrameLoader() {
  if (mMessageManager) {
    mMessageManager->Disconnect();
  }

  MOZ_ASSERT(!mOwnerContent);
  MOZ_RELEASE_ASSERT(mDestroyCalled);
}

static nsAtom* TypeAttrName(Element* aOwnerContent) {
  return aOwnerContent->IsXULElement() ? nsGkAtoms::type
                                       : nsGkAtoms::mozframetype;
}

static void GetFrameName(Element* aOwnerContent, nsAString& aFrameName) {
  int32_t namespaceID = aOwnerContent->GetNameSpaceID();
  if (namespaceID == kNameSpaceID_XHTML && !aOwnerContent->IsInHTMLDocument()) {
    aOwnerContent->GetAttr(nsGkAtoms::id, aFrameName);
  } else {
    aOwnerContent->GetAttr(nsGkAtoms::name, aFrameName);
    // XXX if no NAME then use ID, after a transition period this will be
    // changed so that XUL only uses ID too (bug 254284).
    if (aFrameName.IsEmpty() && namespaceID == kNameSpaceID_XUL) {
      aOwnerContent->GetAttr(nsGkAtoms::id, aFrameName);
    }
  }
}

// If this method returns true, the nsFrameLoader will act as a boundary, as is
// the case for <iframe mozbrowser> and <browser type="content"> elements.
//
// # Historical Notes  (10 April 2019)
//
// In the past, this boundary was defined by the "typeContent" and "typeChrome"
// nsIDocShellTreeItem types. There was only ever a single split in the tree,
// and it occurred at the boundary between these two types of docshells. When
// <iframe mozbrowser> was introduced, it was given special casing to make it
// act like a second boundary, without having to change the existing code.
//
// The about:addons page, which is loaded within a content browser, then added a
// remote <browser type="content" remote="true"> element. When remote, this
// would also act as a mechanism for creating a disjoint tree, due to the
// process keeping the embedder and embedee separate.
//
// However, when initial out-of-process iframe support was implemented, this
// codepath became a risk, as it could've caused the oop iframe remote
// WindowProxy code to be activated for the addons page. This was fixed by
// extendng the isolation logic previously reserved to <iframe mozbrowser> to
// also cover <browser> elements with the explicit `remote` property loaded in
// content.
//
// To keep these boundaries clear, and allow them to work in a cross-process
// manner, they are no longer handled by typeContent and typeChrome. Instead,
// the actual BrowsingContext tree is broken at these edges.
static bool IsTopContent(BrowsingContext* aParent, Element* aOwner) {
  if (XRE_IsContentProcess()) {
    return false;
  }

  if (aParent->IsContent()) {
    // If we're already in content, we may still want to create a new
    // BrowsingContext tree if our element is a xul browser element with a
    // `remote="true"` marker.
    return aOwner->IsXULElement() &&
           aOwner->AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
                               nsGkAtoms::_true, eCaseMatters);
  }

  // If we're in a chrome context, we want to start a new tree if we are an
  // element with a `type="content"` marker.
  return aOwner->AttrValueIs(kNameSpaceID_None, TypeAttrName(aOwner),
                             nsGkAtoms::content, eIgnoreCase);
}

static already_AddRefed<BrowsingContext> CreateBrowsingContext(
    Element* aOwner, nsIOpenWindowInfo* aOpenWindowInfo,
    BrowsingContextGroup* aSpecificGroup, bool aNetworkCreated = false) {
  MOZ_ASSERT(!aOpenWindowInfo || !aSpecificGroup,
             "Only one of SpecificGroup and OpenWindowInfo may be provided!");

  // If we've got a pending BrowserParent from the content process, use the
  // BrowsingContext which was created for it.
  if (aOpenWindowInfo && aOpenWindowInfo->GetNextRemoteBrowser()) {
    MOZ_ASSERT(XRE_IsParentProcess());
    return do_AddRef(
        aOpenWindowInfo->GetNextRemoteBrowser()->GetBrowsingContext());
  }

  RefPtr<BrowsingContext> opener;
  if (aOpenWindowInfo && !aOpenWindowInfo->GetForceNoOpener()) {
    opener = aOpenWindowInfo->GetParent();
    if (opener) {
      // Must create BrowsingContext with opener in-process.
      MOZ_ASSERT(opener->IsInProcess());

      // This can only happen when the opener was closed from a nested event
      // loop in the window provider code, and only when the open was triggered
      // by a non-e10s tab, and the new tab is being opened in a new browser
      // window. Since it is a corner case among corner cases, and the opener
      // window will appear to be null to consumers after it is discarded
      // anyway, just drop the opener entirely.
      if (opener->IsDiscarded()) {
        NS_WARNING(
            "Opener was closed from a nested event loop in the parent process. "
            "Please fix this.");
        opener = nullptr;
      }
    }
  }

  RefPtr<nsGlobalWindowInner> parentInner =
      nsGlobalWindowInner::Cast(aOwner->OwnerDoc()->GetInnerWindow());
  if (NS_WARN_IF(!parentInner) || parentInner->IsDying()) {
    return nullptr;
  }

  BrowsingContext* parentBC = parentInner->GetBrowsingContext();
  if (NS_WARN_IF(!parentBC) || parentBC->IsDiscarded()) {
    return nullptr;
  }

  // Determine the frame name for the new browsing context.
  nsAutoString frameName;
  GetFrameName(aOwner, frameName);

  // Create our BrowsingContext without immediately attaching it. It's possible
  // that no DocShell or remote browser will ever be created for this
  // FrameLoader, particularly if the document that we were created for is not
  // currently active. And in that latter case, if we try to attach our BC now,
  // it will wind up attached as a child of the currently active inner window
  // for the BrowsingContext, and cause no end of trouble.
  if (IsTopContent(parentBC, aOwner)) {
    BrowsingContext::CreateDetachedOptions options;
    if (aOpenWindowInfo) {
      options.topLevelCreatedByWebContent =
          aOpenWindowInfo->GetIsTopLevelCreatedByWebContent();
    }
    options.windowless = parentBC->Windowless();

    // Create toplevel context without a parent & as Type::Content.
    return BrowsingContext::CreateDetached(
        nullptr, opener, aSpecificGroup, frameName,
        BrowsingContext::Type::Content, options);
  }

  MOZ_ASSERT(!aOpenWindowInfo,
             "Can't have openWindowInfo for non-toplevel context");

  MOZ_ASSERT(!aSpecificGroup,
             "Can't force BrowsingContextGroup for non-toplevel context");
  return BrowsingContext::CreateDetached(
      parentInner, nullptr, nullptr, frameName, parentBC->GetType(),
      {.createdDynamically = !aNetworkCreated,
       .windowless = parentBC->Windowless()});
}

static bool InitialLoadIsRemote(Element* aOwner) {
  // The initial load in an content process iframe should never be made remote.
  // Content process iframes always become remote due to navigation.
  if (XRE_IsContentProcess()) {
    return false;
  }

  // Otherwise, we're remote if we have "remote=true" and we're a XUL element.
  return (aOwner->GetNameSpaceID() == kNameSpaceID_XUL) &&
         aOwner->AttrValueIs(kNameSpaceID_None, nsGkAtoms::remote,
                             nsGkAtoms::_true, eCaseMatters);
}

static already_AddRefed<BrowsingContextGroup> InitialBrowsingContextGroup(
    Element* aOwner) {
  nsAutoString attrString;
  if (aOwner->GetNameSpaceID() != kNameSpaceID_XUL ||
      !aOwner->GetAttr(nsGkAtoms::initialBrowsingContextGroupId, attrString)) {
    return nullptr;
  }

  // It's OK to read the attribute using a signed 64-bit integer parse, as an ID
  // generated using `nsContentUtils::GenerateProcessSpecificId` (like BCG IDs)
  // will only ever use 53 bits of precision, so it can be round-tripped through
  // a JS number.
  nsresult rv = NS_OK;
  int64_t signedGroupId = attrString.ToInteger64(&rv, 10);
  if (NS_FAILED(rv) || signedGroupId <= 0) {
    MOZ_DIAGNOSTIC_ASSERT(
        false, "we intended to have a particular id, but failed to parse it!");
    return nullptr;
  }

  return BrowsingContextGroup::GetOrCreate(uint64_t(signedGroupId));
}

already_AddRefed<nsFrameLoader> nsFrameLoader::Create(
    Element* aOwner, bool aNetworkCreated, nsIOpenWindowInfo* aOpenWindowInfo) {
  NS_ENSURE_TRUE(aOwner, nullptr);
  Document* doc = aOwner->OwnerDoc();

  // We never create nsFrameLoaders for elements in resource documents.
  //
  // We never create nsFrameLoaders for elements in data documents, unless the
  // document is a static document.
  // Static documents are an exception because any sub-documents need an
  // nsFrameLoader to keep the relevant docShell alive, even though the
  // nsFrameLoader isn't used to load anything (the sub-document is created by
  // the static clone process).
  //
  // We never create nsFrameLoaders for elements that are not
  // in-composed-document, unless the element belongs to a static document.
  // Static documents are an exception because this method is called at a point
  // in the static clone process before aOwner has been inserted into its
  // document.  For other types of documents this wouldn't be a problem since
  // we'd create the nsFrameLoader as necessary after aOwner is inserted into a
  // document, but the mechanisms that take care of that don't apply for static
  // documents so we need to create the nsFrameLoader now. (This isn't wasteful
  // since for a static document we know aOwner will end up in a document and
  // the nsFrameLoader will be used for its docShell.)
  //
  NS_ENSURE_TRUE(!doc->IsResourceDoc() &&
                     ((!doc->IsLoadedAsData() && aOwner->IsInComposedDoc()) ||
                      doc->IsStaticDocument()),
                 nullptr);

  RefPtr<BrowsingContextGroup> group = InitialBrowsingContextGroup(aOwner);
  RefPtr<BrowsingContext> context =
      CreateBrowsingContext(aOwner, aOpenWindowInfo, group, aNetworkCreated);
  NS_ENSURE_TRUE(context, nullptr);

  if (XRE_IsParentProcess() && aOpenWindowInfo) {
    MOZ_ASSERT(context->IsTopContent());
    if (RefPtr<BrowsingContext> crossGroupOpener =
            aOpenWindowInfo->GetParent()) {
      context->Canonical()->SetCrossGroupOpenerId(crossGroupOpener->Id());
    }
  }

  bool isRemoteFrame = InitialLoadIsRemote(aOwner);
  RefPtr<nsFrameLoader> fl =
      new nsFrameLoader(aOwner, context, isRemoteFrame, aNetworkCreated);
  fl->mOpenWindowInfo = aOpenWindowInfo;

  // If this is a toplevel initial remote frame, we're looking at a browser
  // loaded in the parent process. Pull the remote type attribute off of the
  // <browser> element to determine which remote type it should be loaded in, or
  // use `DEFAULT_REMOTE_TYPE` if we can't tell.
  if (isRemoteFrame) {
    MOZ_ASSERT(XRE_IsParentProcess());
    nsAutoString remoteType;
    if (aOwner->GetAttr(nsGkAtoms::RemoteType, remoteType) &&
        !remoteType.IsEmpty()) {
      CopyUTF16toUTF8(remoteType, fl->mRemoteType);
    } else {
      fl->mRemoteType = DEFAULT_REMOTE_TYPE;
    }
  }
  return fl.forget();
}

/* static */
already_AddRefed<nsFrameLoader> nsFrameLoader::Recreate(
    mozilla::dom::Element* aOwner, BrowsingContext* aContext,
    BrowsingContextGroup* aSpecificGroup,
    const NavigationIsolationOptions& aRemotenessOptions, bool aIsRemote,
    bool aNetworkCreated, bool aPreserveContext) {
  NS_ENSURE_TRUE(aOwner, nullptr);

#ifdef DEBUG
  // This version of Create is only called for Remoteness updates, so we can
  // assume we need a FrameLoader here and skip the check in the other Create.
  Document* doc = aOwner->OwnerDoc();
  MOZ_ASSERT(!doc->IsResourceDoc());
  MOZ_ASSERT((!doc->IsLoadedAsData() && aOwner->IsInComposedDoc()) ||
             doc->IsStaticDocument());
#endif

  RefPtr<BrowsingContext> context = aContext;
  if (!context || !aPreserveContext) {
    context = CreateBrowsingContext(aOwner, /* openWindowInfo */ nullptr,
                                    aSpecificGroup);
    if (aContext) {
      MOZ_ASSERT(
          XRE_IsParentProcess(),
          "Recreating browing contexts only supported in the parent process");
      aContext->Canonical()->SynchronizeLayoutHistoryState();
      aContext->Canonical()->ReplacedBy(context->Canonical(),
                                        aRemotenessOptions);
    }
  }
  NS_ENSURE_TRUE(context, nullptr);

  RefPtr<nsFrameLoader> fl =
      new nsFrameLoader(aOwner, context, aIsRemote, aNetworkCreated);
  return fl.forget();
}

void nsFrameLoader::LoadFrame(bool aOriginalSrc,
                              bool aShouldCheckForRecursion) {
  if (NS_WARN_IF(!mOwnerContent)) {
    return;
  }

  nsAutoString src;
  nsCOMPtr<nsIPrincipal> principal;
  nsCOMPtr<nsIContentSecurityPolicy> csp;

  bool isSrcdoc = mOwnerContent->IsHTMLElement(nsGkAtoms::iframe) &&
                  mOwnerContent->HasAttr(nsGkAtoms::srcdoc);
  if (isSrcdoc) {
    src.AssignLiteral("about:srcdoc");
    principal = mOwnerContent->NodePrincipal();
    csp = mOwnerContent->GetCsp();
  } else {
    GetURL(src, getter_AddRefs(principal), getter_AddRefs(csp));

    src.Trim(" \t\n\r");

    if (src.IsEmpty()) {
      // If the frame is a XUL element and has the attribute 'nodefaultsrc=true'
      // then we will not use 'about:blank' as fallback but return early without
      // starting a load if no 'src' attribute is given (or it's empty).
      if (mOwnerContent->IsXULElement() &&
          mOwnerContent->AttrValueIs(kNameSpaceID_None, nsGkAtoms::nodefaultsrc,
                                     nsGkAtoms::_true, eCaseMatters)) {
        return;
      }
      src.AssignLiteral("about:blank");
      principal = mOwnerContent->NodePrincipal();
      csp = mOwnerContent->GetCsp();
    }
  }

  Document* doc = mOwnerContent->OwnerDoc();
  if (doc->IsStaticDocument()) {
    return;
  }

  // If we are being loaded by a lazy loaded iframe, use its base URI first
  // instead of the current base URI.
  auto* lazyBaseURI = GetLazyLoadFrameResumptionState().mBaseURI.get();
  nsIURI* baseURI = lazyBaseURI ? lazyBaseURI : mOwnerContent->GetBaseURI();

  auto encoding = doc->GetDocumentCharacterSet();

  nsCOMPtr<nsIURI> uri;
  nsresult rv = NS_NewURI(getter_AddRefs(uri), src, encoding, baseURI);

  // If the URI was malformed, try to recover by loading about:blank.
  if (rv == NS_ERROR_MALFORMED_URI) {
    rv = NS_NewURI(getter_AddRefs(uri), u"about:blank"_ns, encoding, baseURI);
  }

  if (NS_SUCCEEDED(rv)) {
    rv = LoadURI(uri, principal, csp, aOriginalSrc, aShouldCheckForRecursion);
  }

  if (NS_FAILED(rv)) {
    FireErrorEvent();
  }
}

void nsFrameLoader::ConfigRemoteProcess(const nsACString& aRemoteType,
                                        ContentParent* aContentParent) {
  MOZ_DIAGNOSTIC_ASSERT(IsRemoteFrame(), "Must be a remote frame");
  MOZ_DIAGNOSTIC_ASSERT(!mRemoteBrowser, "Must not have a browser yet");
  MOZ_DIAGNOSTIC_ASSERT_IF(aContentParent,
                           aContentParent->GetRemoteType() == aRemoteType);

  mRemoteType = aRemoteType;
  mChildID = aContentParent ? aContentParent->ChildID() : 0;
}

void nsFrameLoader::FireErrorEvent() {
  if (!mOwnerContent) {
    return;
  }
  RefPtr<AsyncEventDispatcher> loadBlockingAsyncDispatcher =
      new LoadBlockingAsyncEventDispatcher(
          mOwnerContent, u"error"_ns, CanBubble::eNo, ChromeOnlyDispatch::eNo);
  loadBlockingAsyncDispatcher->PostDOMEvent();
}

nsresult nsFrameLoader::LoadURI(nsIURI* aURI,
                                nsIPrincipal* aTriggeringPrincipal,
                                nsIContentSecurityPolicy* aCsp,
                                bool aOriginalSrc,
                                bool aShouldCheckForRecursion) {
  if (!aURI) return NS_ERROR_INVALID_POINTER;
  NS_ENSURE_STATE(!mDestroyCalled && mOwnerContent);
  MOZ_ASSERT(
      aTriggeringPrincipal,
      "Must have an explicit triggeringPrincipal to nsFrameLoader::LoadURI.");

  mLoadingOriginalSrc = aOriginalSrc;
  mShouldCheckForRecursion = aShouldCheckForRecursion;

  nsCOMPtr<Document> doc = mOwnerContent->OwnerDoc();

  nsresult rv;
  rv = CheckURILoad(aURI, aTriggeringPrincipal);
  NS_ENSURE_SUCCESS(rv, rv);

  mURIToLoad = aURI;
  mTriggeringPrincipal = aTriggeringPrincipal;
  mCsp = aCsp;
  rv = doc->InitializeFrameLoader(this);
  if (NS_FAILED(rv)) {
    mURIToLoad = nullptr;
    mTriggeringPrincipal = nullptr;
    mCsp = nullptr;
  }
  return rv;
}

void nsFrameLoader::ResumeLoad(uint64_t aPendingSwitchID) {
  Document* doc = mOwnerContent->OwnerDoc();
  if (doc->IsStaticDocument()) {
    // Static doc shouldn't load sub-documents.
    return;
  }

  if (NS_WARN_IF(mDestroyCalled || !mOwnerContent)) {
    FireErrorEvent();
    return;
  }

  mLoadingOriginalSrc = false;
  mShouldCheckForRecursion = false;
  mURIToLoad = nullptr;
  mPendingSwitchID = aPendingSwitchID;
  mTriggeringPrincipal = mOwnerContent->NodePrincipal();
  mCsp = mOwnerContent->GetCsp();

  nsresult rv = doc->InitializeFrameLoader(this);
  if (NS_FAILED(rv)) {
    mPendingSwitchID = 0;
    mTriggeringPrincipal = nullptr;
    mCsp = nullptr;

    FireErrorEvent();
  }
}

nsresult nsFrameLoader::ReallyStartLoading() {
  nsresult rv = ReallyStartLoadingInternal();
  if (NS_FAILED(rv)) {
    FireErrorEvent();
  }

  return rv;
}

nsresult nsFrameLoader::ReallyStartLoadingInternal() {
  NS_ENSURE_STATE((mURIToLoad || mPendingSwitchID) && mOwnerContent &&
                  mOwnerContent->IsInComposedDoc());

  AUTO_PROFILER_LABEL("nsFrameLoader::ReallyStartLoadingInternal", OTHER);
  RefPtr<nsDocShellLoadState> loadState;
  if (!mPendingSwitchID) {
    loadState = new nsDocShellLoadState(mURIToLoad);
    loadState->SetOriginalFrameSrc(mLoadingOriginalSrc);
    loadState->SetShouldCheckForRecursion(mShouldCheckForRecursion);

    // The triggering principal could be null if the frame is loaded other
    // than the src attribute, for example, the frame is sandboxed. In that
    // case we use the principal of the owner content, which is needed to
    // prevent XSS attaches on documents loaded in subframes.
    if (mTriggeringPrincipal) {
      loadState->SetTriggeringPrincipal(mTriggeringPrincipal);
    } else {
      loadState->SetTriggeringPrincipal(mOwnerContent->NodePrincipal());
    }

    // If we have an explicit CSP, we set it. If not, we only query it from
    // the document in case there was no explicit triggeringPrincipal.
    // Otherwise it's possible that the original triggeringPrincipal did not
    // have a CSP which causes the CSP on the Principal and explicit CSP
    // to be out of sync.
    if (mCsp) {
      loadState->SetCsp(mCsp);
    } else if (!mTriggeringPrincipal) {
      nsCOMPtr<nsIContentSecurityPolicy> csp = mOwnerContent->GetCsp();
      loadState->SetCsp(csp);
    }

    nsAutoString srcdoc;
    bool isSrcdoc = mOwnerContent->IsHTMLElement(nsGkAtoms::iframe) &&
                    mOwnerContent->GetAttr(nsGkAtoms::srcdoc, srcdoc);

    if (isSrcdoc) {
      loadState->SetSrcdocData(srcdoc);
      loadState->SetBaseURI(mOwnerContent->GetBaseURI());
    }

    auto referrerInfo = MakeRefPtr<ReferrerInfo>(
        *mOwnerContent, GetLazyLoadFrameResumptionState().mReferrerPolicy);
    loadState->SetReferrerInfo(referrerInfo);

    loadState->SetIsFromProcessingFrameAttributes();

    // Default flags:
    int32_t flags = nsIWebNavigation::LOAD_FLAGS_NONE;
    loadState->SetLoadFlags(flags);

    loadState->SetFirstParty(false);

    Document* ownerDoc = mOwnerContent->OwnerDoc();
    if (ownerDoc) {
      loadState->SetTriggeringStorageAccess(ownerDoc->UsingStorageAccess());
      loadState->SetTriggeringWindowId(ownerDoc->InnerWindowID());
    }

    // If we're loading the default about:blank document in a <browser> element,
    // prevent the load from causing a process switch by explicitly overriding
    // remote type selection.
    if (mPendingBrowsingContext->IsTopContent() &&
        mOwnerContent->IsXULElement(nsGkAtoms::browser) &&
        NS_IsAboutBlank(mURIToLoad) &&
        loadState->TriggeringPrincipal()->IsSystemPrincipal()) {
      loadState->SetRemoteTypeOverride(mRemoteType);
    }
  }

  if (IsRemoteFrame()) {
    if (!EnsureRemoteBrowser()) {
      NS_WARNING("Couldn't create child process for iframe.");
      return NS_ERROR_FAILURE;
    }

    if (mPendingSwitchID) {
      mRemoteBrowser->ResumeLoad(mPendingSwitchID);
      mPendingSwitchID = 0;
    } else {
      mRemoteBrowser->LoadURL(loadState);
    }

    if (!mRemoteBrowserShown) {
      // This can fail if it's too early to show the frame, we will retry later.
      Unused << ShowRemoteFrame(
          /* aFrame = */ do_QueryFrame(GetPrimaryFrameOfOwningContent()));
    }

    return NS_OK;
  }

  nsresult rv = MaybeCreateDocShell();
  if (NS_FAILED(rv)) {
    return rv;
  }
  MOZ_ASSERT(GetDocShell(),
             "MaybeCreateDocShell succeeded with a null docShell");

  // If we have a pending switch, just resume our load.
  if (mPendingSwitchID) {
    bool tmpState = mNeedsAsyncDestroy;
    mNeedsAsyncDestroy = true;
    rv = GetDocShell()->ResumeRedirectedLoad(mPendingSwitchID, -1);
    mNeedsAsyncDestroy = tmpState;
    mPendingSwitchID = 0;
    return rv;
  }

  // Just to be safe, recheck uri.
  rv = CheckURILoad(mURIToLoad, mTriggeringPrincipal);
  NS_ENSURE_SUCCESS(rv, rv);

  mLoadingOriginalSrc = false;
  mShouldCheckForRecursion = false;

  // Kick off the load...
  bool tmpState = mNeedsAsyncDestroy;
  mNeedsAsyncDestroy = true;

  RefPtr<nsDocShell> docShell = GetDocShell();
  rv = docShell->LoadURI(loadState, false);
  mNeedsAsyncDestroy = tmpState;
  mURIToLoad = nullptr;
  NS_ENSURE_SUCCESS(rv, rv);

  return NS_OK;
}

nsresult nsFrameLoader::CheckURILoad(nsIURI* aURI,
                                     nsIPrincipal* aTriggeringPrincipal) {
  // Check for security.  The fun part is trying to figure out what principals
  // to use.  The way I figure it, if we're doing a LoadFrame() accidentally
  // (eg someone created a frame/iframe node, we're being parsed, XUL iframes
  // are being reframed, etc.) then we definitely want to use the node
  // principal of mOwnerContent for security checks.  If, on the other hand,
  // someone's setting the src on our owner content, or created it via script,
  // or whatever, then they can clearly access it... and we should still use
  // the principal of mOwnerContent.  I don't think that leads to privilege
  // escalation, and it's reasonably guaranteed to not lead to XSS issues
  // (since caller can already access mOwnerContent in this case).  So just use
  // the principal of mOwnerContent no matter what.  If script wants to run
  // things with its own permissions, which differ from those of mOwnerContent
  // (which means the script is privileged in some way) it should set
  // window.location instead.
  nsIScriptSecurityManager* secMan = nsContentUtils::GetSecurityManager();

  // Get our principal
  nsIPrincipal* principal =
      (aTriggeringPrincipal ? aTriggeringPrincipal
                            : mOwnerContent->NodePrincipal());

  // Check if we are allowed to load absURL
  nsresult rv = secMan->CheckLoadURIWithPrincipal(
      principal, aURI, nsIScriptSecurityManager::STANDARD,
      mOwnerContent->OwnerDoc()->InnerWindowID());
  if (NS_FAILED(rv)) {
    return rv;  // We're not
  }

  // Bail out if this is an infinite recursion scenario
  if (IsRemoteFrame()) {
    return NS_OK;
  }
  return CheckForRecursiveLoad(aURI);
}

nsDocShell* nsFrameLoader::GetDocShell(ErrorResult& aRv) {
  if (IsRemoteFrame()) {
    return nullptr;
  }

  // If we have an owner, make sure we have a docshell and return
  // that. If not, we're most likely in the middle of being torn down,
  // then we just return null.
  if (mOwnerContent) {
    nsresult rv = MaybeCreateDocShell();
    if (NS_FAILED(rv)) {
      aRv.Throw(rv);
      return nullptr;
    }
    MOZ_ASSERT(GetDocShell(),
               "MaybeCreateDocShell succeeded, but null docShell");
  }

  return GetDocShell();
}

static void SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
    nsIDocShellTreeItem* aItem, nsIDocShellTreeOwner* aOwner,
    EventTarget* aHandler) {
  MOZ_ASSERT(aItem, "Must have item");

  aItem->SetTreeOwner(aOwner);

  int32_t childCount = 0;
  aItem->GetInProcessChildCount(&childCount);
  for (int32_t i = 0; i < childCount; ++i) {
    nsCOMPtr<nsIDocShellTreeItem> item;
    aItem->GetInProcessChildAt(i, getter_AddRefs(item));
    if (aHandler) {
      nsCOMPtr<nsIDocShell> shell(do_QueryInterface(item));
      shell->SetChromeEventHandler(aHandler);
    }
    SetTreeOwnerAndChromeEventHandlerOnDocshellTree(item, aOwner, aHandler);
  }
}

#if defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)
static bool CheckDocShellType(mozilla::dom::Element* aOwnerContent,
                              nsIDocShellTreeItem* aDocShell, nsAtom* aAtom) {
  bool isContent = aOwnerContent->AttrValueIs(kNameSpaceID_None, aAtom,
                                              nsGkAtoms::content, eIgnoreCase);

  if (isContent) {
    return aDocShell->ItemType() == nsIDocShellTreeItem::typeContent;
  }

  nsCOMPtr<nsIDocShellTreeItem> parent;
  aDocShell->GetInProcessParent(getter_AddRefs(parent));

  return parent && parent->ItemType() == aDocShell->ItemType();
}
#endif  // defined(MOZ_DIAGNOSTIC_ASSERT_ENABLED)

/**
* Hook up a given TreeItem to its tree owner. aItem's type must have already
* been set, and it should already be part of the DocShellTree.
* @param aItem the treeitem we're working with
* @param aTreeOwner the relevant treeowner; might be null
*/
void nsFrameLoader::AddTreeItemToTreeOwner(nsIDocShellTreeItem* aItem,
                                           nsIDocShellTreeOwner* aOwner) {
  MOZ_ASSERT(aItem, "Must have docshell treeitem");
  MOZ_ASSERT(mOwnerContent, "Must have owning content");

  MOZ_DIAGNOSTIC_ASSERT(
      CheckDocShellType(mOwnerContent, aItem, TypeAttrName(mOwnerContent)),
      "Correct ItemType should be set when creating BrowsingContext");

  if (mIsTopLevelContent) {
    bool is_primary = mOwnerContent->AttrValueIs(
        kNameSpaceID_None, nsGkAtoms::primary, nsGkAtoms::_true, eIgnoreCase);
    if (aOwner) {
      mOwnerContent->AddMutationObserver(this);
      mObservingOwnerContent = true;
      aOwner->ContentShellAdded(aItem, is_primary);
    }
  }
}

static bool AllDescendantsOfType(BrowsingContext* aParent,
                                 BrowsingContext::Type aType) {
  for (auto& child : aParent->Children()) {
    if (child->GetType() != aType || !AllDescendantsOfType(child, aType)) {
      return false;
    }
  }

  return true;
}

void nsFrameLoader::MaybeShowFrame() {
  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
  if (frame) {
    nsSubDocumentFrame* subDocFrame = do_QueryFrame(frame);
    if (subDocFrame) {
      subDocFrame->MaybeShowViewer();
    }
  }
}

static ScrollbarPreference GetScrollbarPreference(const Element* aOwner) {
  if (!aOwner) {
    return ScrollbarPreference::Auto;
  }
  const nsAttrValue* attrValue = aOwner->GetParsedAttr(nsGkAtoms::scrolling);
  return nsGenericHTMLFrameElement::MapScrollingAttribute(attrValue);
}

static CSSIntSize GetMarginAttributes(const Element* aOwner) {
  CSSIntSize result(-1, -1);
  auto* content = nsGenericHTMLElement::FromNodeOrNull(aOwner);
  if (!content) {
    return result;
  }
  const nsAttrValue* attr = content->GetParsedAttr(nsGkAtoms::marginwidth);
  if (attr && attr->Type() == nsAttrValue::eInteger) {
    result.width = attr->GetIntegerValue();
  }
  attr = content->GetParsedAttr(nsGkAtoms::marginheight);
  if (attr && attr->Type() == nsAttrValue::eInteger) {
    result.height = attr->GetIntegerValue();
  }
  return result;
}

bool nsFrameLoader::Show(nsSubDocumentFrame* aFrame) {
  if (mInShow) {
    return false;
  }
  mInShow = true;

  auto resetInShow = mozilla::MakeScopeExit([&] { mInShow = false; });
  if (IsRemoteFrame()) {
    return ShowRemoteFrame(aFrame);
  }
  const LayoutDeviceIntSize size = aFrame->GetInitialSubdocumentSize();
  nsresult rv = MaybeCreateDocShell();
  if (NS_FAILED(rv)) {
    return false;
  }
  nsDocShell* ds = GetDocShell();
  MOZ_ASSERT(ds, "MaybeCreateDocShell succeeded, but null docShell");
  if (!ds) {
    return false;
  }

  ds->SetScrollbarPreference(GetScrollbarPreference(mOwnerContent));
  const bool marginsChanged =
      ds->UpdateFrameMargins(GetMarginAttributes(mOwnerContent));

  nsView* view = aFrame->EnsureInnerView();
  if (!view) {
    return false;
  }

  // If we already have a pres shell (which can happen with <object> / <embed>)
  // then hook it up in the view tree.
  if (PresShell* presShell = ds->GetPresShell()) {
    // Ensure root scroll frame is reflowed in case margins have changed.
    if (marginsChanged) {
      if (nsIFrame* rootScrollContainerFrame =
              presShell->GetRootScrollContainerFrame()) {
        presShell->FrameNeedsReflow(rootScrollContainerFrame,
                                    IntrinsicDirty::None, NS_FRAME_IS_DIRTY);
      }
    }
    nsView* childView = presShell->GetViewManager()->GetRootView();
    MOZ_DIAGNOSTIC_ASSERT(childView);
    if (childView->GetParent() == view) {
      // We were probably doing a docshell swap and succeeded before getting
      // here, hooray, nothing else to do.
      return true;
    }

    // We did layout before due to <object> or <embed> and now we need to fix
    // up our stuff and initialize our docshell below too.
    MOZ_DIAGNOSTIC_ASSERT(!view->GetFirstChild());
    MOZ_DIAGNOSTIC_ASSERT(!childView->GetParent(), "Stale view?");
    nsSubDocumentFrame::InsertViewsInReverseOrder(childView, view);
    nsSubDocumentFrame::EndSwapDocShellsForViews(view->GetFirstChild());
  }

  RefPtr<nsDocShell> baseWindow = GetDocShell();
  baseWindow->InitWindow(view->GetWidget(), 0, 0, size.width, size.height);
  baseWindow->SetVisibility(true);
  NS_ENSURE_TRUE(GetDocShell(), false);

  // Trigger editor re-initialization if midas is turned on in the sub-document.
  // This shouldn't be necessary, but given the way our editor works, it is.
  //
  // See https://bugzilla.mozilla.org/show_bug.cgi?id=284245
  //
  // FIXME(emilio): This is a massive hack, plus probably not the right place to
  // do it. Should probably be done in Document::CreatePresShell?
  if (RefPtr<PresShell> presShell = GetDocShell()->GetPresShell()) {
    Document* doc = presShell->GetDocument();
    nsHTMLDocument* htmlDoc =
        doc && doc->IsHTMLOrXHTML() ? doc->AsHTMLDocument() : nullptr;

    if (htmlDoc) {
      nsAutoString designMode;
      htmlDoc->GetDesignMode(designMode);

      if (designMode.EqualsLiteral("on")) {
        // Hold on to the editor object to let the document reattach to the
        // same editor object, instead of creating a new one.
        RefPtr<HTMLEditor> htmlEditor = GetDocShell()->GetHTMLEditor();
        Unused << htmlEditor;
        htmlDoc->SetDesignMode(u"off"_ns, Nothing(), IgnoreErrors());

        htmlDoc->SetDesignMode(u"on"_ns, Nothing(), IgnoreErrors());
      } else {
        // Re-initialize the presentation for contenteditable documents
        bool editable = false, hasEditingSession = false;
        GetDocShell()->GetEditable(&editable);
        GetDocShell()->GetHasEditingSession(&hasEditingSession);
        RefPtr<HTMLEditor> htmlEditor = GetDocShell()->GetHTMLEditor();
        if (editable && hasEditingSession && htmlEditor) {
          htmlEditor->PostCreate();
        }
      }
    }
  }

  mInShow = false;
  if (mHideCalled) {
    mHideCalled = false;
    Hide();
    return false;
  }
  return true;
}

void nsFrameLoader::MarginsChanged() {
  // We assume that the margins are always zero for remote frames.
  if (IsRemoteFrame()) {
    return;
  }

  nsDocShell* docShell = GetDocShell();
  // If there's no docshell, we're probably not up and running yet.
  // nsFrameLoader::Show() will take care of setting the right
  // margins.
  if (!docShell) {
    return;
  }

  if (!docShell->UpdateFrameMargins(GetMarginAttributes(mOwnerContent))) {
    return;
  }

  // There's a cached property declaration block
  // that needs to be updated
  if (Document* doc = docShell->GetDocument()) {
    for (nsINode* cur = doc; cur; cur = cur->GetNextNode()) {
      if (auto* body = HTMLBodyElement::FromNode(cur)) {
        body->FrameMarginsChanged();
      }
    }
  }
}

bool nsFrameLoader::ShowRemoteFrame(nsSubDocumentFrame* aFrame) {
  AUTO_PROFILER_LABEL("nsFrameLoader::ShowRemoteFrame", OTHER);
  NS_ASSERTION(IsRemoteFrame(),
               "ShowRemote only makes sense on remote frames.");

  if (!EnsureRemoteBrowser()) {
    NS_ERROR("Couldn't create child process.");
    return false;
  }

  const bool hasSize =
      aFrame && !aFrame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW);

  // FIXME/bug 589337: Show()/Hide() is pretty expensive for
  // cross-process layers; need to figure out what behavior we really
  // want here.  For now, hack.
  if (!mRemoteBrowserShown) {
    if (!mOwnerContent || !mOwnerContent->GetComposedDoc()) {
      return false;
    }

    // We never want to host remote frameloaders in simple popups, like menus.
    nsIWidget* widget = nsContentUtils::WidgetForContent(mOwnerContent);
    if (!widget || static_cast<nsBaseWidget*>(widget)->IsSmallPopup()) {
      return false;
    }

    if (BrowserHost* bh = mRemoteBrowser->AsBrowserHost()) {
      RefPtr<BrowsingContext> bc = bh->GetBrowsingContext()->Top();

      // Set to the current activation of the window.
      bc->SetIsActiveBrowserWindow(bc->GetIsActiveBrowserWindow());
    }

    nsCOMPtr<nsISupports> container = mOwnerContent->OwnerDoc()->GetContainer();
    nsCOMPtr<nsIBaseWindow> baseWindow = do_QueryInterface(container);
    nsCOMPtr<nsIWidget> mainWidget;
    baseWindow->GetMainWidget(getter_AddRefs(mainWidget));
    nsSizeMode sizeMode =
        mainWidget ? mainWidget->SizeMode() : nsSizeMode_Normal;
    const auto size =
        hasSize ? aFrame->GetSubdocumentSize() : LayoutDeviceIntSize();
    OwnerShowInfo info(size, GetScrollbarPreference(mOwnerContent), sizeMode);
    if (!mRemoteBrowser->Show(info)) {
      return false;
    }
    mRemoteBrowserShown = true;
    mRemoteBrowserSized = hasSize;

    // This notification doesn't apply to fission, apparently.
    if (!GetBrowserBridgeChild()) {
      if (nsCOMPtr<nsIObserverService> os = services::GetObserverService()) {
        os->NotifyObservers(ToSupports(this), "remote-browser-shown", nullptr);
      }
    }
  } else if (hasSize) {
    NS_ENSURE_SUCCESS(UpdatePositionAndSize(aFrame), false);
  }

  return true;
}

void nsFrameLoader::Hide() {
  if (mHideCalled) {
    return;
  }
  if (mInShow) {
    mHideCalled = true;
    return;
  }

  if (mRemoteBrowser) {
    mRemoteBrowser->UpdateEffects(EffectsInfo::FullyHidden());
  }

  if (!GetDocShell()) {
    return;
  }

  nsCOMPtr<nsIDocumentViewer> viewer;
  GetDocShell()->GetDocViewer(getter_AddRefs(viewer));
  if (viewer) viewer->SetSticky(false);

  RefPtr<nsDocShell> baseWin = GetDocShell();
  baseWin->SetVisibility(false);
  baseWin->SetParentWidget(nullptr);
}

void nsFrameLoader::ForceLayoutIfNecessary() {
  nsIFrame* frame = GetPrimaryFrameOfOwningContent();
  if (!frame) {
    return;
  }

  nsPresContext* presContext = frame->PresContext();
  if (!presContext) {
    return;
  }

  // Only force the layout flush if the frameloader hasn't ever been
  // run through layout.
  if (frame->HasAnyStateBits(NS_FRAME_FIRST_REFLOW)) {
    if (RefPtr<PresShell> presShell = presContext->GetPresShell()) {
      presShell->FlushPendingNotifications(FlushType::Layout);
    }
  }
}

nsresult nsFrameLoader::SwapWithOtherRemoteLoader(
    nsFrameLoader* aOther, nsFrameLoaderOwner* aThisOwner,
    nsFrameLoaderOwner* aOtherOwner) {
  MOZ_ASSERT(NS_IsMainThread());

#ifdef DEBUG
  RefPtr<nsFrameLoader> first = aThisOwner->GetFrameLoader();
  RefPtr<nsFrameLoader> second = aOtherOwner->GetFrameLoader();
  MOZ_ASSERT(first == this, "aThisOwner must own this");
  MOZ_ASSERT(second == aOther, "aOtherOwner must own aOther");
#endif

  Element* ourContent = mOwnerContent;
  Element* otherContent = aOther->mOwnerContent;

  if (!ourContent || !otherContent) {
    // Can't handle this
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // Make sure there are no same-origin issues
  bool equal;
  nsresult rv = ourContent->NodePrincipal()->Equals(
      otherContent->NodePrincipal(), &equal);
  if (NS_FAILED(rv) || !equal) {
    // Security problems loom.  Just bail on it all
    return NS_ERROR_DOM_SECURITY_ERR;
  }

  Document* ourDoc = ourContent->GetComposedDoc();
  Document* otherDoc = otherContent->GetComposedDoc();
  if (!ourDoc || !otherDoc) {
    // Again, how odd, given that we had docshells
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  PresShell* ourPresShell = ourDoc->GetPresShell();
  PresShell* otherPresShell = otherDoc->GetPresShell();
  if (!ourPresShell || !otherPresShell) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  auto* browserParent = GetBrowserParent();
  auto* otherBrowserParent = aOther->GetBrowserParent();

  if (!browserParent || !otherBrowserParent) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  RefPtr<BrowsingContext> ourBc = browserParent->GetBrowsingContext();
  RefPtr<BrowsingContext> otherBc = otherBrowserParent->GetBrowsingContext();

  // When we swap docShells, maybe we have to deal with a new page created just
  // for this operation. In this case, the browser code should already have set
  // the correct userContextId attribute value in the owning element, but our
  // docShell, that has been created way before) doesn't know that that
  // happened.
  // This is the reason why now we must retrieve the correct value from the
  // usercontextid attribute before comparing our originAttributes with the
  // other one.
  OriginAttributes ourOriginAttributes = ourBc->OriginAttributesRef();
  rv = PopulateOriginContextIdsFromAttributes(ourOriginAttributes);
  NS_ENSURE_SUCCESS(rv, rv);

  OriginAttributes otherOriginAttributes = otherBc->OriginAttributesRef();
  rv = aOther->PopulateOriginContextIdsFromAttributes(otherOriginAttributes);
  NS_ENSURE_SUCCESS(rv, rv);

  if (!ourOriginAttributes.EqualsIgnoringFPD(otherOriginAttributes)) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  bool ourHasHistory = mIsTopLevelContent &&
                       ourContent->IsXULElement(nsGkAtoms::browser) &&
                       !ourContent->HasAttr(nsGkAtoms::disablehistory);
  bool otherHasHistory = aOther->mIsTopLevelContent &&
                         otherContent->IsXULElement(nsGkAtoms::browser) &&
                         !otherContent->HasAttr(nsGkAtoms::disablehistory);
  if (ourHasHistory != otherHasHistory) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  if (mInSwap || aOther->mInSwap) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }
  mInSwap = aOther->mInSwap = true;

  // NOTE(emilio): This doesn't have to flush because the caller does already.
  nsIFrame* ourFrame = ourContent->GetPrimaryFrame();
  nsIFrame* otherFrame = otherContent->GetPrimaryFrame();
  if (!ourFrame || !otherFrame) {
    mInSwap = aOther->mInSwap = false;
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  nsSubDocumentFrame* ourFrameFrame = do_QueryFrame(ourFrame);
  if (!ourFrameFrame) {
    mInSwap = aOther->mInSwap = false;
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  rv = ourFrameFrame->BeginSwapDocShells(otherFrame);
  if (NS_FAILED(rv)) {
    mInSwap = aOther->mInSwap = false;
    return rv;
  }

  nsCOMPtr<nsIBrowserDOMWindow> otherBrowserDOMWindow =
      otherBrowserParent->GetBrowserDOMWindow();
  nsCOMPtr<nsIBrowserDOMWindow> browserDOMWindow =
      browserParent->GetBrowserDOMWindow();

  if (!!otherBrowserDOMWindow != !!browserDOMWindow) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  otherBrowserParent->SetBrowserDOMWindow(browserDOMWindow);
  browserParent->SetBrowserDOMWindow(otherBrowserDOMWindow);

  MaybeUpdatePrimaryBrowserParent(eBrowserParentRemoved);
  aOther->MaybeUpdatePrimaryBrowserParent(eBrowserParentRemoved);

  if (mozilla::BFCacheInParent() && XRE_IsParentProcess()) {
    // nsFrameLoaders in session history can't be moved to another owner since
    // there are no corresponging message managers on which swap can be done.
    // See the line mMessageManager.swap(aOther->mMessageManager); below.
    auto evict = [](nsFrameLoader* aFrameLoader) {
      if (BrowsingContext* bc =
              aFrameLoader->GetMaybePendingBrowsingContext()) {
        nsCOMPtr<nsISHistory> shistory = bc->Canonical()->GetSessionHistory();
        if (shistory) {
          shistory->EvictAllDocumentViewers();
        }
      }
    };
    evict(this);
    evict(aOther);
  }

  SetOwnerContent(otherContent);
  aOther->SetOwnerContent(ourContent);

  browserParent->SetOwnerElement(otherContent);
  otherBrowserParent->SetOwnerElement(ourContent);

  // Update window activation state for the swapped owner content.
  bool ourActive = otherBc->GetIsActiveBrowserWindow();
  bool otherActive = ourBc->GetIsActiveBrowserWindow();
  if (ourBc->IsTop()) {
    ourBc->SetIsActiveBrowserWindow(otherActive);
  }
  if (otherBc->IsTop()) {
    otherBc->SetIsActiveBrowserWindow(ourActive);
  }

  MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);
  aOther->MaybeUpdatePrimaryBrowserParent(eBrowserParentChanged);

  RefPtr<nsFrameMessageManager> ourMessageManager = mMessageManager;
  RefPtr<nsFrameMessageManager> otherMessageManager = aOther->mMessageManager;
  // Swap and setup things in parent message managers.
  if (ourMessageManager) {
    ourMessageManager->SetCallback(aOther);
  }
  if (otherMessageManager) {
    otherMessageManager->SetCallback(this);
  }
  mMessageManager.swap(aOther->mMessageManager);

  // XXXsmaug what should be done to JSWindowActorParent objects when swapping
  // frameloaders? Currently they leak very easily, bug 1697918.

  // Perform the actual swap of the internal refptrs. We keep a strong reference
  // to ourselves to make sure we don't die while we overwrite our reference to
  // ourself.
  RefPtr<nsFrameLoader> kungFuDeathGrip(this);
  aThisOwner->SetFrameLoader(aOther);
  aOtherOwner->SetFrameLoader(kungFuDeathGrip);

  ourFrameFrame->EndSwapDocShells(otherFrame);

  ourPresShell->BackingScaleFactorChanged();
  otherPresShell->BackingScaleFactorChanged();

  mInSwap = aOther->mInSwap = false;

  // Send an updated tab context since owner content type may have changed.
  MutableTabContext ourContext;
  rv = GetNewTabContext(&ourContext);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }
  MutableTabContext otherContext;
  rv = aOther->GetNewTabContext(&otherContext);
  if (NS_WARN_IF(NS_FAILED(rv))) {
    return rv;
  }

  Unused << browserParent->SendSwappedWithOtherRemoteLoader(
      ourContext.AsIPCTabContext());
  Unused << otherBrowserParent->SendSwappedWithOtherRemoteLoader(
      otherContext.AsIPCTabContext());
  // These might have moved to a new window, so make sure they have
  // the appropriate priority (bug 1896172)
  browserParent->RecomputeProcessPriority();
  otherBrowserParent->RecomputeProcessPriority();
  return NS_OK;
}

class MOZ_RAII AutoResetInFrameSwap final {
public:
  AutoResetInFrameSwap(nsFrameLoader* aThisFrameLoader,
                       nsFrameLoader* aOtherFrameLoader,
                       nsDocShell* aThisDocShell, nsDocShell* aOtherDocShell,
                       EventTarget* aThisEventTarget,
                       EventTarget* aOtherEventTarget)
      : mThisFrameLoader(aThisFrameLoader),
        mOtherFrameLoader(aOtherFrameLoader),
        mThisDocShell(aThisDocShell),
        mOtherDocShell(aOtherDocShell),
        mThisEventTarget(aThisEventTarget),
        mOtherEventTarget(aOtherEventTarget) {
    mThisFrameLoader->mInSwap = true;
    mOtherFrameLoader->mInSwap = true;
    mThisDocShell->SetInFrameSwap(true);
    mOtherDocShell->SetInFrameSwap(true);

    // Fire pageshow events on still-loading pages, and then fire pagehide
    // events.  Note that we do NOT fire these in the normal way, but just fire
    // them on the chrome event handlers.
    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
        mThisDocShell, mThisEventTarget, false);
    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
        mOtherDocShell, mOtherEventTarget, false);
    nsContentUtils::FirePageHideEventForFrameLoaderSwap(mThisDocShell,
                                                        mThisEventTarget);
    nsContentUtils::FirePageHideEventForFrameLoaderSwap(mOtherDocShell,
                                                        mOtherEventTarget);
  }

  ~AutoResetInFrameSwap() {
    nsContentUtils::FirePageShowEventForFrameLoaderSwap(mThisDocShell,
                                                        mThisEventTarget, true);
    nsContentUtils::FirePageShowEventForFrameLoaderSwap(
        mOtherDocShell, mOtherEventTarget, true);

    mThisFrameLoader->mInSwap = false;
    mOtherFrameLoader->mInSwap = false;
    mThisDocShell->SetInFrameSwap(false);
    mOtherDocShell->SetInFrameSwap(false);

    // This is needed to get visibility state right in cases when we swapped a
    // visible tab (foreground in visible window) with a non-visible tab.
    if (RefPtr<Document> doc = mThisDocShell->GetDocument()) {
      doc->UpdateVisibilityState();
    }
    if (RefPtr<Document> doc = mOtherDocShell->GetDocument()) {
      doc->UpdateVisibilityState();
    }
  }

private:
  RefPtr<nsFrameLoader> mThisFrameLoader;
  RefPtr<nsFrameLoader> mOtherFrameLoader;
  RefPtr<nsDocShell> mThisDocShell;
  RefPtr<nsDocShell> mOtherDocShell;
  nsCOMPtr<EventTarget> mThisEventTarget;
  nsCOMPtr<EventTarget> mOtherEventTarget;
};

nsresult nsFrameLoader::SwapWithOtherLoader(nsFrameLoader* aOther,
                                            nsFrameLoaderOwner* aThisOwner,
                                            nsFrameLoaderOwner* aOtherOwner) {
#ifdef DEBUG
  RefPtr<nsFrameLoader> first = aThisOwner->GetFrameLoader();
  RefPtr<nsFrameLoader> second = aOtherOwner->GetFrameLoader();
  MOZ_ASSERT(first == this, "aThisOwner must own this");
  MOZ_ASSERT(second == aOther, "aOtherOwner must own aOther");
#endif

  NS_ENSURE_STATE(!mInShow && !aOther->mInShow);

  if (IsRemoteFrame() != aOther->IsRemoteFrame()) {
    NS_WARNING(
        "Swapping remote and non-remote frames is not currently supported");
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  RefPtr<Element> ourContent = mOwnerContent;
  RefPtr<Element> otherContent = aOther->mOwnerContent;
  if (!ourContent || !otherContent) {
    // Can't handle this
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  nsIFrame* ourFrame = ourContent->GetPrimaryFrame(FlushType::Frames);
  nsIFrame* otherFrame = otherContent->GetPrimaryFrame(FlushType::Frames);
  if (!ourFrame || !otherFrame) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // Ensure the flushes above haven't changed all the world.
  if (ourContent != mOwnerContent || otherContent != aOther->mOwnerContent) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  bool ourHasSrcdoc = ourContent->IsHTMLElement(nsGkAtoms::iframe) &&
                      ourContent->HasAttr(nsGkAtoms::srcdoc);
  bool otherHasSrcdoc = otherContent->IsHTMLElement(nsGkAtoms::iframe) &&
                        otherContent->HasAttr(nsGkAtoms::srcdoc);
  if (ourHasSrcdoc || otherHasSrcdoc) {
    // Ignore this case entirely for now, since we support XUL <-> HTML swapping
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  bool ourFullscreenAllowed = ourContent->IsXULElement();
  bool otherFullscreenAllowed = otherContent->IsXULElement();
  if (ourFullscreenAllowed != otherFullscreenAllowed) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  nsILoadContext* ourLoadContext = ourContent->OwnerDoc()->GetLoadContext();
  nsILoadContext* otherLoadContext = otherContent->OwnerDoc()->GetLoadContext();
  MOZ_ASSERT(ourLoadContext && otherLoadContext,
             "Swapping frames within dead documents?");
  if (ourLoadContext->UseRemoteTabs() != otherLoadContext->UseRemoteTabs()) {
    NS_WARNING("Can't swap between e10s and non-e10s windows");
    return NS_ERROR_NOT_IMPLEMENTED;
  }
  if (ourLoadContext->UseRemoteSubframes() !=
      otherLoadContext->UseRemoteSubframes()) {
    NS_WARNING("Can't swap between fission and non-fission windows");
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // Divert to a separate path for the remaining steps in the remote case
  if (IsRemoteFrame()) {
    MOZ_ASSERT(aOther->IsRemoteFrame());
    return SwapWithOtherRemoteLoader(aOther, aThisOwner, aOtherOwner);
  }

  // Make sure there are no same-origin issues
  bool equal;
  nsresult rv = ourContent->NodePrincipal()->Equals(
      otherContent->NodePrincipal(), &equal);
  if (NS_FAILED(rv) || !equal) {
    // Security problems loom.  Just bail on it all
    return NS_ERROR_DOM_SECURITY_ERR;
  }

  RefPtr<nsDocShell> ourDocshell = GetExistingDocShell();
  RefPtr<nsDocShell> otherDocshell = aOther->GetExistingDocShell();
  if (!ourDocshell || !otherDocshell) {
    // How odd
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // To avoid having to mess with session history, avoid swapping
  // frameloaders that don't correspond to root same-type docshells,
  // unless both roots have session history disabled.
  nsCOMPtr<nsIDocShellTreeItem> ourRootTreeItem, otherRootTreeItem;
  ourDocshell->GetInProcessSameTypeRootTreeItem(
      getter_AddRefs(ourRootTreeItem));
  otherDocshell->GetInProcessSameTypeRootTreeItem(
      getter_AddRefs(otherRootTreeItem));
  nsCOMPtr<nsIWebNavigation> ourRootWebnav = do_QueryInterface(ourRootTreeItem);
  nsCOMPtr<nsIWebNavigation> otherRootWebnav =
      do_QueryInterface(otherRootTreeItem);

  if (!ourRootWebnav || !otherRootWebnav) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  RefPtr<ChildSHistory> ourHistory = ourRootWebnav->GetSessionHistory();
  RefPtr<ChildSHistory> otherHistory = otherRootWebnav->GetSessionHistory();

  if ((ourRootTreeItem != ourDocshell || otherRootTreeItem != otherDocshell) &&
      (ourHistory || otherHistory)) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  RefPtr<BrowsingContext> ourBc = ourDocshell->GetBrowsingContext();
  RefPtr<BrowsingContext> otherBc = otherDocshell->GetBrowsingContext();

  // Also make sure that the two BrowsingContexts are the same type. Otherwise
  // swapping is certainly not safe. If this needs to be changed then
  // the code below needs to be audited as it assumes identical types.
  if (ourBc->GetType() != otherBc->GetType()) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // We ensure that BCs are either both top frames or both subframes.
  if (ourBc->IsTop() != otherBc->IsTop()) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // One more twist here.  Setting up the right treeowners in a heterogeneous
  // tree is a bit of a pain.  So make sure that if `ourBc->GetType()` is not
  // nsIDocShellTreeItem::typeContent then all of our descendants are the same
  // type as us.
  if (!ourBc->IsContent() &&
      (!AllDescendantsOfType(ourBc, ourBc->GetType()) ||
       !AllDescendantsOfType(otherBc, otherBc->GetType()))) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // Save off the tree owners, frame elements, chrome event handlers, and
  // docshell and document parents before doing anything else.
  nsCOMPtr<nsIDocShellTreeOwner> ourOwner, otherOwner;
  ourDocshell->GetTreeOwner(getter_AddRefs(ourOwner));
  otherDocshell->GetTreeOwner(getter_AddRefs(otherOwner));
  // Note: it's OK to have null treeowners.

  nsCOMPtr<nsIDocShellTreeItem> ourParentItem, otherParentItem;
  ourDocshell->GetInProcessParent(getter_AddRefs(ourParentItem));
  otherDocshell->GetInProcessParent(getter_AddRefs(otherParentItem));
  if (!ourParentItem || !otherParentItem) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  nsCOMPtr<nsPIDOMWindowOuter> ourWindow = ourDocshell->GetWindow();
  nsCOMPtr<nsPIDOMWindowOuter> otherWindow = otherDocshell->GetWindow();

  nsCOMPtr<Element> ourFrameElement = ourWindow->GetFrameElementInternal();
  nsCOMPtr<Element> otherFrameElement = otherWindow->GetFrameElementInternal();

  nsCOMPtr<EventTarget> ourChromeEventHandler =
      ourWindow->GetChromeEventHandler();
  nsCOMPtr<EventTarget> otherChromeEventHandler =
      otherWindow->GetChromeEventHandler();

  nsCOMPtr<EventTarget> ourEventTarget = ourWindow->GetParentTarget();
  nsCOMPtr<EventTarget> otherEventTarget = otherWindow->GetParentTarget();

  NS_ASSERTION(SameCOMIdentity(ourFrameElement, ourContent) &&
                   SameCOMIdentity(otherFrameElement, otherContent) &&
                   SameCOMIdentity(ourChromeEventHandler, ourContent) &&
                   SameCOMIdentity(otherChromeEventHandler, otherContent),
               "How did that happen, exactly?");

  nsCOMPtr<Document> ourChildDocument = ourWindow->GetExtantDoc();
  nsCOMPtr<Document> otherChildDocument = otherWindow->GetExtantDoc();
  if (!ourChildDocument || !otherChildDocument) {
    // This shouldn't be happening
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  nsCOMPtr<Document> ourParentDocument =
      ourChildDocument->GetInProcessParentDocument();
  nsCOMPtr<Document> otherParentDocument =
      otherChildDocument->GetInProcessParentDocument();

  // Make sure to swap docshells between the two frames.
  Document* ourDoc = ourContent->GetComposedDoc();
  Document* otherDoc = otherContent->GetComposedDoc();
  if (!ourDoc || !otherDoc) {
    // Again, how odd, given that we had docshells
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  NS_ASSERTION(ourDoc == ourParentDocument, "Unexpected parent document");
  NS_ASSERTION(otherDoc == otherParentDocument, "Unexpected parent document");

  PresShell* ourPresShell = ourDoc->GetPresShell();
  PresShell* otherPresShell = otherDoc->GetPresShell();
  if (!ourPresShell || !otherPresShell) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // When we swap docShells, maybe we have to deal with a new page created just
  // for this operation. In this case, the browser code should already have set
  // the correct userContextId attribute value in the owning element, but our
  // docShell, that has been created way before) doesn't know that that
  // happened.
  // This is the reason why now we must retrieve the correct value from the
  // usercontextid attribute before comparing our originAttributes with the
  // other one.
  OriginAttributes ourOriginAttributes = ourDocshell->GetOriginAttributes();
  rv = PopulateOriginContextIdsFromAttributes(ourOriginAttributes);
  NS_ENSURE_SUCCESS(rv, rv);

  OriginAttributes otherOriginAttributes = otherDocshell->GetOriginAttributes();
  rv = aOther->PopulateOriginContextIdsFromAttributes(otherOriginAttributes);
  NS_ENSURE_SUCCESS(rv, rv);

  if (ourOriginAttributes != otherOriginAttributes) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  if (mInSwap || aOther->mInSwap) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }
  AutoResetInFrameSwap autoFrameSwap(this, aOther, ourDocshell, otherDocshell,
                                     ourEventTarget, otherEventTarget);

  nsSubDocumentFrame* ourFrameFrame = do_QueryFrame(ourFrame);
  if (!ourFrameFrame) {
    return NS_ERROR_NOT_IMPLEMENTED;
  }

  // OK.  First begin to swap the docshells in the two nsIFrames
  rv = ourFrameFrame->BeginSwapDocShells(otherFrame);
  if (NS_FAILED(rv)) {
    return rv;
  }

  // Now move the docshells to the right docshell trees.  Note that this
  // resets their treeowners to null.
  ourParentItem->RemoveChild(ourDocshell);
  otherParentItem->RemoveChild(otherDocshell);
  if (ourBc->IsContent()) {
    ourOwner->ContentShellRemoved(ourDocshell);
    otherOwner->ContentShellRemoved(otherDocshell);
  }

  ourParentItem->AddChild(otherDocshell);
  otherParentItem->AddChild(ourDocshell);

  // Restore the correct chrome event handlers.
  ourDocshell->SetChromeEventHandler(otherChromeEventHandler);
  otherDocshell->SetChromeEventHandler(ourChromeEventHandler);
  // Restore the correct treeowners
  // (and also chrome event handlers for content frames only).
  SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
      ourDocshell, otherOwner,
      ourBc->IsContent() ? otherChromeEventHandler.get() : nullptr);
  SetTreeOwnerAndChromeEventHandlerOnDocshellTree(
      otherDocshell, ourOwner,
      ourBc->IsContent() ? ourChromeEventHandler.get() : nullptr);

  // Switch the owner content before we start calling AddTreeItemToTreeOwner.
  // Note that we rely on this to deal with setting mObservingOwnerContent to
  // false and calling RemoveMutationObserver as needed.
  SetOwnerContent(otherContent);
  aOther->SetOwnerContent(ourContent);

  AddTreeItemToTreeOwner(ourDocshell, otherOwner);
  aOther->AddTreeItemToTreeOwner(otherDocshell, ourOwner);

  // SetSubDocumentFor nulls out parent documents on the old child doc if a
  // new non-null document is passed in, so just go ahead and remove both
  // kids before reinserting in the parent subdoc maps, to avoid
  // complications.
  ourParentDocument->SetSubDocumentFor(ourContent, nullptr);
  otherParentDocument->SetSubDocumentFor(otherContent, nullptr);
  ourParentDocument->SetSubDocumentFor(ourContent, otherChildDocument);
  otherParentDocument->SetSubDocumentFor(otherContent, ourChildDocument);

  ourWindow->SetFrameElementInternal(otherFrameElement);
  otherWindow->SetFrameElementInternal(ourFrameElement);

  RefPtr<nsFrameMessageManager> ourMessageManager = mMessageManager;
  RefPtr<nsFrameMessageManager> otherMessageManager = aOther->mMessageManager;
  // Swap pointers in child message managers.
  if (mChildMessageManager) {
    InProcessBrowserChildMessageManager* browserChild = mChildMessageManager;
    browserChild->SetOwner(otherContent);
    browserChild->SetChromeMessageManager(otherMessageManager);
  }
  if (aOther->mChildMessageManager) {
    InProcessBrowserChildMessageManager* otherBrowserChild =
        aOther->mChildMessageManager;
    otherBrowserChild->SetOwner(ourContent);
    otherBrowserChild->SetChromeMessageManager(ourMessageManager);
  }
  // Swap and setup things in parent message managers.
  if (mMessageManager) {
    mMessageManager->SetCallback(aOther);
  }
  if (aOther->mMessageManager) {
    aOther->mMessageManager->SetCallback(this);
  }
  mMessageManager.swap(aOther->mMessageManager);

  // Perform the actual swap of the internal refptrs. We keep a strong reference
  // to ourselves to make sure we don't die while we overwrite our reference to
  // ourself.
  RefPtr<nsFrameLoader> kungFuDeathGrip(this);
  aThisOwner->SetFrameLoader(aOther);
  aOtherOwner->SetFrameLoader(kungFuDeathGrip);

  // Drop any cached content viewers in the two session histories.
  if (ourHistory) {
--> --------------------

--> maximum size reached

--> --------------------

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