Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2066 insertions, 0 deletions

diff --git a/dom/base/FragmentOrElement.cpp b/dom/base/FragmentOrElement.cpp
new file mode 100644
index 0000000000..9811ce5ace
--- /dev/null
+++ b/dom/base/FragmentOrElement.cpp
@@ -0,0 +1,2066 @@
+/* -*- 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/. */
+
+/*
+ * Base class for all element classes and DocumentFragment.
+ */
+
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/StaticPtr.h"
+
+#include "mozilla/dom/FragmentOrElement.h"
+#include "DOMIntersectionObserver.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/DeclarationBlock.h"
+#include "mozilla/EffectSet.h"
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/EventListenerManager.h"
+#include "mozilla/ElementAnimationData.h"
+#include "mozilla/HTMLEditor.h"
+#include "mozilla/mozInlineSpellChecker.h"
+#include "mozilla/PresShell.h"
+#include "mozilla/RestyleManager.h"
+#include "mozilla/TextEditor.h"
+#include "mozilla/TouchEvents.h"
+#include "mozilla/URLExtraData.h"
+#include "mozilla/dom/Attr.h"
+#include "mozilla/dom/RadioGroupContainer.h"
+#include "nsDOMAttributeMap.h"
+#include "nsAtom.h"
+#include "mozilla/dom/NodeInfo.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/ScriptLoader.h"
+#include "mozilla/dom/TouchEvent.h"
+#include "mozilla/dom/CustomElementRegistry.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DocumentInlines.h"
+#include "nsIControllers.h"
+#include "nsIDocumentEncoder.h"
+#include "nsFocusManager.h"
+#include "nsIScriptGlobalObject.h"
+#include "nsNetUtil.h"
+#include "nsIFrame.h"
+#include "nsIAnonymousContentCreator.h"
+#include "nsPresContext.h"
+#include "nsStyleConsts.h"
+#include "nsString.h"
+#include "nsUnicharUtils.h"
+#include "nsDOMCID.h"
+#include "nsDOMCSSAttrDeclaration.h"
+#include "nsNameSpaceManager.h"
+#include "nsContentList.h"
+#include "nsDOMTokenList.h"
+#include "nsError.h"
+#include "nsDOMString.h"
+#include "nsXULElement.h"
+#include "mozilla/InternalMutationEvent.h"
+#include "mozilla/MouseEvents.h"
+#include "nsAttrValueOrString.h"
+#include "nsQueryObject.h"
+#include "nsFrameSelection.h"
+#ifdef DEBUG
+#  include "nsRange.h"
+#endif
+
+#include "nsFrameLoader.h"
+#include "nsPIDOMWindow.h"
+#include "nsLayoutUtils.h"
+#include "nsGkAtoms.h"
+#include "nsContentUtils.h"
+#include "nsTextFragment.h"
+#include "nsContentCID.h"
+#include "nsWindowSizes.h"
+
+#include "nsIWidget.h"
+
+#include "nsNodeInfoManager.h"
+#include "nsGenericHTMLElement.h"
+#include "nsContentCreatorFunctions.h"
+#include "nsView.h"
+#include "nsViewManager.h"
+#include "nsIScrollableFrame.h"
+#include "ChildIterator.h"
+#include "nsTextNode.h"
+#include "mozilla/dom/NodeListBinding.h"
+
+#include "nsCCUncollectableMarker.h"
+
+#include "mozAutoDocUpdate.h"
+
+#include "mozilla/Sprintf.h"
+#include "nsDOMMutationObserver.h"
+#include "nsWrapperCacheInlines.h"
+#include "nsCycleCollector.h"
+#include "xpcpublic.h"
+#include "mozilla/Telemetry.h"
+
+#include "mozilla/CORSMode.h"
+
+#include "mozilla/dom/ShadowRoot.h"
+#include "mozilla/dom/HTMLSlotElement.h"
+#include "mozilla/dom/HTMLTemplateElement.h"
+#include "mozilla/dom/SVGUseElement.h"
+
+#include "nsStyledElement.h"
+#include "nsIContentInlines.h"
+#include "nsChildContentList.h"
+#include "mozilla/BloomFilter.h"
+
+#include "NodeUbiReporting.h"
+
+#ifdef ACCESSIBILITY
+#  include "nsAccessibilityService.h"
+#endif
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+int32_t nsIContent::sTabFocusModel = eTabFocus_any;
+bool nsIContent::sTabFocusModelAppliesToXUL = false;
+uint64_t nsMutationGuard::sGeneration = 0;
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsIContent)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsIContent)
+  MOZ_ASSERT_UNREACHABLE("Our subclasses don't call us");
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsIContent)
+  MOZ_ASSERT_UNREACHABLE("Our subclasses don't call us");
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN(nsIContent)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  // Don't bother to QI to cycle collection, because our CC impl is
+  // not doing anything anyway.
+  NS_INTERFACE_MAP_ENTRY(nsIContent)
+  NS_INTERFACE_MAP_ENTRY(nsINode)
+  NS_INTERFACE_MAP_ENTRY(mozilla::dom::EventTarget)
+  NS_INTERFACE_MAP_ENTRY_TEAROFF(nsISupportsWeakReference,
+                                 new nsNodeSupportsWeakRefTearoff(this))
+  // DOM bindings depend on the identity pointer being the
+  // same as nsINode (which nsIContent inherits).
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsIContent)
+
+NS_IMPL_DOMARENA_DESTROY(nsIContent)
+
+NS_IMPL_CYCLE_COLLECTING_RELEASE_WITH_LAST_RELEASE_AND_DESTROY(nsIContent,
+                                                               LastRelease(),
+                                                               Destroy())
+
+nsIContent* nsIContent::FindFirstNonChromeOnlyAccessContent() const {
+  // This handles also nested native anonymous content.
+  for (const nsIContent* content = this; content;
+       content = content->GetChromeOnlyAccessSubtreeRootParent()) {
+    if (!content->ChromeOnlyAccess()) {
+      // Oops, this function signature allows casting const to
+      // non-const.  (Then again, so does GetFirstChild()->GetParent().)
+      return const_cast<nsIContent*>(content);
+    }
+  }
+  return nullptr;
+}
+
+// https://dom.spec.whatwg.org/#dom-slotable-assignedslot
+HTMLSlotElement* nsIContent::GetAssignedSlotByMode() const {
+  /**
+   * Get slotable's assigned slot for the result of
+   * find a slot with open flag UNSET [1].
+   *
+   * [1] https://dom.spec.whatwg.org/#assign-a-slot
+   */
+  HTMLSlotElement* slot = GetAssignedSlot();
+  if (!slot) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(GetParent());
+  MOZ_ASSERT(GetParent()->GetShadowRoot());
+
+  /**
+   * Additional check for open flag SET:
+   *   If slotable’s parent’s shadow root's mode is not "open",
+   *   then return null.
+   */
+  if (GetParent()->GetShadowRoot()->IsClosed()) {
+    return nullptr;
+  }
+
+  return slot;
+}
+
+nsIContent::IMEState nsIContent::GetDesiredIMEState() {
+  if (!IsEditable()) {
+    // Check for the special case where we're dealing with elements which don't
+    // have the editable flag set, but are readwrite (such as text controls).
+    if (!IsElement() ||
+        !AsElement()->State().HasState(ElementState::READWRITE)) {
+      return IMEState(IMEEnabled::Disabled);
+    }
+  }
+  // NOTE: The content for independent editors (e.g., input[type=text],
+  // textarea) must override this method, so, we don't need to worry about
+  // that here.
+  nsIContent* editableAncestor = GetEditingHost();
+
+  // This is in another editable content, use the result of it.
+  if (editableAncestor && editableAncestor != this) {
+    return editableAncestor->GetDesiredIMEState();
+  }
+  Document* doc = GetComposedDoc();
+  if (!doc) {
+    return IMEState(IMEEnabled::Disabled);
+  }
+  nsPresContext* pc = doc->GetPresContext();
+  if (!pc) {
+    return IMEState(IMEEnabled::Disabled);
+  }
+  HTMLEditor* htmlEditor = nsContentUtils::GetHTMLEditor(pc);
+  if (!htmlEditor) {
+    return IMEState(IMEEnabled::Disabled);
+  }
+  IMEState state;
+  htmlEditor->GetPreferredIMEState(&state);
+  return state;
+}
+
+bool nsIContent::HasIndependentSelection() const {
+  nsIFrame* frame = GetPrimaryFrame();
+  return (frame && frame->HasAnyStateBits(NS_FRAME_INDEPENDENT_SELECTION));
+}
+
+dom::Element* nsIContent::GetEditingHost() {
+  // If this isn't editable, return nullptr.
+  if (!IsEditable()) {
+    return nullptr;
+  }
+
+  Document* doc = GetComposedDoc();
+  if (!doc) {
+    return nullptr;
+  }
+
+  // If this is in designMode, we should return <body>
+  if (IsInDesignMode() && !IsInShadowTree()) {
+    return doc->GetBodyElement();
+  }
+
+  dom::Element* editableParentElement = nullptr;
+  for (dom::Element* parent = GetParentElement();
+       parent && parent->HasFlag(NODE_IS_EDITABLE);
+       parent = editableParentElement->GetParentElement()) {
+    editableParentElement = parent;
+  }
+  return editableParentElement ? editableParentElement
+                               : dom::Element::FromNode(this);
+}
+
+nsresult nsIContent::LookupNamespaceURIInternal(
+    const nsAString& aNamespacePrefix, nsAString& aNamespaceURI) const {
+  if (aNamespacePrefix.EqualsLiteral("xml")) {
+    // Special-case for xml prefix
+    aNamespaceURI.AssignLiteral("http://www.w3.org/XML/1998/namespace");
+    return NS_OK;
+  }
+
+  if (aNamespacePrefix.EqualsLiteral("xmlns")) {
+    // Special-case for xmlns prefix
+    aNamespaceURI.AssignLiteral("http://www.w3.org/2000/xmlns/");
+    return NS_OK;
+  }
+
+  RefPtr<nsAtom> name;
+  if (!aNamespacePrefix.IsEmpty()) {
+    name = NS_Atomize(aNamespacePrefix);
+    NS_ENSURE_TRUE(name, NS_ERROR_OUT_OF_MEMORY);
+  } else {
+    name = nsGkAtoms::xmlns;
+  }
+  // Trace up the content parent chain looking for the namespace
+  // declaration that declares aNamespacePrefix.
+  for (Element* element = GetAsElementOrParentElement(); element;
+       element = element->GetParentElement()) {
+    if (element->GetAttr(kNameSpaceID_XMLNS, name, aNamespaceURI)) {
+      return NS_OK;
+    }
+  }
+  return NS_ERROR_FAILURE;
+}
+
+nsAtom* nsIContent::GetLang() const {
+  for (const Element* element = GetAsElementOrParentElement(); element;
+       element = element->GetParentElement()) {
+    if (!element->GetAttrCount()) {
+      continue;
+    }
+
+    // xml:lang has precedence over lang on HTML elements (see
+    // XHTML1 section C.7).
+    const nsAttrValue* attr =
+        element->GetParsedAttr(nsGkAtoms::lang, kNameSpaceID_XML);
+    if (!attr && element->SupportsLangAttr()) {
+      attr = element->GetParsedAttr(nsGkAtoms::lang);
+    }
+    if (attr) {
+      MOZ_ASSERT(attr->Type() == nsAttrValue::eAtom);
+      MOZ_ASSERT(attr->GetAtomValue());
+      return attr->GetAtomValue();
+    }
+  }
+
+  return nullptr;
+}
+
+nsIURI* nsIContent::GetBaseURI(bool aTryUseXHRDocBaseURI) const {
+  if (SVGUseElement* use = GetContainingSVGUseShadowHost()) {
+    if (URLExtraData* data = use->GetContentURLData()) {
+      return data->BaseURI();
+    }
+  }
+
+  return OwnerDoc()->GetBaseURI(aTryUseXHRDocBaseURI);
+}
+
+nsIURI* nsIContent::GetBaseURIForStyleAttr() const {
+  if (SVGUseElement* use = GetContainingSVGUseShadowHost()) {
+    if (URLExtraData* data = use->GetContentURLData()) {
+      return data->BaseURI();
+    }
+  }
+  // This also ignores the case that SVG inside XBL binding.
+  // But it is probably fine.
+  return OwnerDoc()->GetDocBaseURI();
+}
+
+already_AddRefed<URLExtraData> nsIContent::GetURLDataForStyleAttr(
+    nsIPrincipal* aSubjectPrincipal) const {
+  if (SVGUseElement* use = GetContainingSVGUseShadowHost()) {
+    if (URLExtraData* data = use->GetContentURLData()) {
+      return do_AddRef(data);
+    }
+  }
+  auto* doc = OwnerDoc();
+  if (aSubjectPrincipal && aSubjectPrincipal != NodePrincipal()) {
+    nsCOMPtr<nsIReferrerInfo> referrerInfo =
+        doc->ReferrerInfoForInternalCSSAndSVGResources();
+    // TODO: Cache this?
+    return MakeAndAddRef<URLExtraData>(doc->GetDocBaseURI(), referrerInfo,
+                                       aSubjectPrincipal);
+  }
+  return do_AddRef(doc->DefaultStyleAttrURLData());
+}
+
+void nsIContent::ConstructUbiNode(void* storage) {
+  JS::ubi::Concrete<nsIContent>::construct(storage, this);
+}
+
+bool nsIContent::InclusiveDescendantMayNeedSpellchecking(HTMLEditor* aEditor) {
+  // Return true if the node may have elements as children, since those or their
+  // descendants may have spellcheck attributes.
+  return HasFlag(NODE_MAY_HAVE_ELEMENT_CHILDREN) ||
+         mozInlineSpellChecker::ShouldSpellCheckNode(aEditor, this);
+}
+
+//----------------------------------------------------------------------
+
+static inline JSObject* GetJSObjectChild(nsWrapperCache* aCache) {
+  return aCache->PreservingWrapper() ? aCache->GetWrapperPreserveColor()
+                                     : nullptr;
+}
+
+static bool NeedsScriptTraverse(nsINode* aNode) {
+  return aNode->PreservingWrapper() && aNode->GetWrapperPreserveColor() &&
+         !aNode->HasKnownLiveWrapperAndDoesNotNeedTracing(aNode);
+}
+
+//----------------------------------------------------------------------
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsAttrChildContentList)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsAttrChildContentList)
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(nsAttrChildContentList, mNode)
+
+// If the wrapper is known-live, the list can't be part of a garbage cycle.
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(nsAttrChildContentList)
+  return tmp->HasKnownLiveWrapper();
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(nsAttrChildContentList)
+  return tmp->HasKnownLiveWrapperAndDoesNotNeedTracing(tmp);
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(nsAttrChildContentList)
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
+NS_INTERFACE_TABLE_HEAD(nsAttrChildContentList)
+  NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY
+  NS_INTERFACE_TABLE(nsAttrChildContentList, nsINodeList)
+  NS_INTERFACE_TABLE_TO_MAP_SEGUE_CYCLE_COLLECTION(nsAttrChildContentList)
+NS_INTERFACE_MAP_END
+
+JSObject* nsAttrChildContentList::WrapObject(
+    JSContext* cx, JS::Handle<JSObject*> aGivenProto) {
+  return NodeList_Binding::Wrap(cx, this, aGivenProto);
+}
+
+uint32_t nsAttrChildContentList::Length() {
+  return mNode ? mNode->GetChildCount() : 0;
+}
+
+nsIContent* nsAttrChildContentList::Item(uint32_t aIndex) {
+  if (mNode) {
+    return mNode->GetChildAt_Deprecated(aIndex);
+  }
+
+  return nullptr;
+}
+
+int32_t nsAttrChildContentList::IndexOf(nsIContent* aContent) {
+  if (mNode) {
+    return mNode->ComputeIndexOf_Deprecated(aContent);
+  }
+
+  return -1;
+}
+
+//----------------------------------------------------------------------
+uint32_t nsParentNodeChildContentList::Length() {
+  if (!mIsCacheValid && !ValidateCache()) {
+    return 0;
+  }
+
+  MOZ_ASSERT(mIsCacheValid);
+
+  return mCachedChildArray.Length();
+}
+
+nsIContent* nsParentNodeChildContentList::Item(uint32_t aIndex) {
+  if (!mIsCacheValid && !ValidateCache()) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(mIsCacheValid);
+
+  return mCachedChildArray.SafeElementAt(aIndex, nullptr);
+}
+
+int32_t nsParentNodeChildContentList::IndexOf(nsIContent* aContent) {
+  if (!mIsCacheValid && !ValidateCache()) {
+    return -1;
+  }
+
+  MOZ_ASSERT(mIsCacheValid);
+
+  return mCachedChildArray.IndexOf(aContent);
+}
+
+bool nsParentNodeChildContentList::ValidateCache() {
+  MOZ_ASSERT(!mIsCacheValid);
+  MOZ_ASSERT(mCachedChildArray.IsEmpty());
+
+  nsINode* parent = GetParentObject();
+  if (!parent) {
+    return false;
+  }
+
+  for (nsIContent* node = parent->GetFirstChild(); node;
+       node = node->GetNextSibling()) {
+    mCachedChildArray.AppendElement(node);
+  }
+  mIsCacheValid = true;
+
+  return true;
+}
+
+//----------------------------------------------------------------------
+
+nsIHTMLCollection* FragmentOrElement::Children() {
+  nsDOMSlots* slots = DOMSlots();
+
+  if (!slots->mChildrenList) {
+    slots->mChildrenList =
+        new nsContentList(this, kNameSpaceID_Wildcard, nsGkAtoms::_asterisk,
+                          nsGkAtoms::_asterisk, false);
+  }
+
+  return slots->mChildrenList;
+}
+
+//----------------------------------------------------------------------
+
+NS_IMPL_CYCLE_COLLECTION(nsNodeSupportsWeakRefTearoff, mNode)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsNodeSupportsWeakRefTearoff)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END_AGGREGATED(mNode)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsNodeSupportsWeakRefTearoff)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsNodeSupportsWeakRefTearoff)
+
+NS_IMETHODIMP
+nsNodeSupportsWeakRefTearoff::GetWeakReference(
+    nsIWeakReference** aInstancePtr) {
+  nsINode::nsSlots* slots = mNode->Slots();
+  if (!slots->mWeakReference) {
+    slots->mWeakReference = new nsNodeWeakReference(mNode);
+  }
+
+  NS_ADDREF(*aInstancePtr = slots->mWeakReference);
+
+  return NS_OK;
+}
+
+//----------------------------------------------------------------------
+
+static const size_t MaxDOMSlotSizeAllowed =
+#ifdef HAVE_64BIT_BUILD
+    128;
+#else
+    64;
+#endif
+
+static_assert(sizeof(nsINode::nsSlots) <= MaxDOMSlotSizeAllowed,
+              "DOM slots cannot be grown without consideration");
+static_assert(sizeof(FragmentOrElement::nsDOMSlots) <= MaxDOMSlotSizeAllowed,
+              "DOM slots cannot be grown without consideration");
+
+void nsIContent::nsExtendedContentSlots::UnlinkExtendedSlots(nsIContent&) {
+  mContainingShadow = nullptr;
+  mAssignedSlot = nullptr;
+}
+
+void nsIContent::nsExtendedContentSlots::TraverseExtendedSlots(
+    nsCycleCollectionTraversalCallback& aCb) {
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mContainingShadow");
+  aCb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIContent*, mContainingShadow));
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mAssignedSlot");
+  aCb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIContent*, mAssignedSlot.get()));
+}
+
+nsIContent::nsExtendedContentSlots::nsExtendedContentSlots() = default;
+
+nsIContent::nsExtendedContentSlots::~nsExtendedContentSlots() {
+  MOZ_ASSERT(!mManualSlotAssignment);
+}
+
+size_t nsIContent::nsExtendedContentSlots::SizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  // For now, nothing to measure here.  We don't actually own any of our
+  // members.
+  return 0;
+}
+
+FragmentOrElement::nsDOMSlots::nsDOMSlots() : mDataset(nullptr) {
+  MOZ_COUNT_CTOR(nsDOMSlots);
+}
+
+FragmentOrElement::nsDOMSlots::~nsDOMSlots() {
+  MOZ_COUNT_DTOR(nsDOMSlots);
+
+  if (mAttributeMap) {
+    mAttributeMap->DropReference();
+  }
+}
+
+void FragmentOrElement::nsDOMSlots::Traverse(
+    nsCycleCollectionTraversalCallback& aCb) {
+  nsIContent::nsContentSlots::Traverse(aCb);
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mStyle");
+  aCb.NoteXPCOMChild(mStyle.get());
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mAttributeMap");
+  aCb.NoteXPCOMChild(mAttributeMap.get());
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mChildrenList");
+  aCb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsINodeList*, mChildrenList));
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mClassList");
+  aCb.NoteXPCOMChild(mClassList.get());
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mSlots->mPart");
+  aCb.NoteXPCOMChild(mPart.get());
+}
+
+void FragmentOrElement::nsDOMSlots::Unlink(nsINode& aNode) {
+  nsIContent::nsContentSlots::Unlink(aNode);
+  mStyle = nullptr;
+  if (mAttributeMap) {
+    mAttributeMap->DropReference();
+    mAttributeMap = nullptr;
+  }
+  mChildrenList = nullptr;
+  mClassList = nullptr;
+  mPart = nullptr;
+}
+
+size_t FragmentOrElement::nsDOMSlots::SizeOfIncludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  size_t n = aMallocSizeOf(this);
+
+  nsExtendedContentSlots* extendedSlots = GetExtendedContentSlots();
+  if (extendedSlots) {
+    if (OwnsExtendedSlots()) {
+      n += aMallocSizeOf(extendedSlots);
+    }
+
+    n += extendedSlots->SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  if (mAttributeMap) {
+    n += mAttributeMap->SizeOfIncludingThis(aMallocSizeOf);
+  }
+
+  if (mChildrenList) {
+    n += mChildrenList->SizeOfIncludingThis(aMallocSizeOf);
+  }
+
+  // Measurement of the following members may be added later if DMD finds it is
+  // worthwhile:
+  // - Superclass members (nsINode::nsSlots)
+  // - mStyle
+  // - mDataSet
+  // - mClassList
+
+  // The following member are not measured:
+  // - mControllers: because it is non-owning
+  return n;
+}
+
+FragmentOrElement::nsExtendedDOMSlots::nsExtendedDOMSlots() = default;
+
+FragmentOrElement::nsExtendedDOMSlots::~nsExtendedDOMSlots() = default;
+
+void FragmentOrElement::nsExtendedDOMSlots::UnlinkExtendedSlots(
+    nsIContent& aContent) {
+  nsIContent::nsExtendedContentSlots::UnlinkExtendedSlots(aContent);
+
+  // mShadowRoot will similarly be cleared explicitly from
+  // FragmentOrElement::Unlink.
+  mSMILOverrideStyle = nullptr;
+  mControllers = nullptr;
+  mLabelsList = nullptr;
+  mPopoverData = nullptr;
+  if (mCustomElementData) {
+    mCustomElementData->Unlink();
+    mCustomElementData = nullptr;
+  }
+  if (mAnimations) {
+    mAnimations = nullptr;
+    aContent.ClearMayHaveAnimations();
+  }
+  mExplicitlySetAttrElements.Clear();
+  mRadioGroupContainer = nullptr;
+}
+
+void FragmentOrElement::nsExtendedDOMSlots::TraverseExtendedSlots(
+    nsCycleCollectionTraversalCallback& aCb) {
+  nsIContent::nsExtendedContentSlots::TraverseExtendedSlots(aCb);
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mSMILOverrideStyle");
+  aCb.NoteXPCOMChild(mSMILOverrideStyle.get());
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mControllers");
+  aCb.NoteXPCOMChild(mControllers);
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mLabelsList");
+  aCb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsINodeList*, mLabelsList));
+
+  NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "mExtendedSlots->mShadowRoot");
+  aCb.NoteXPCOMChild(NS_ISUPPORTS_CAST(nsIContent*, mShadowRoot));
+
+  if (mCustomElementData) {
+    mCustomElementData->Traverse(aCb);
+  }
+  if (mAnimations) {
+    mAnimations->Traverse(aCb);
+  }
+  if (mRadioGroupContainer) {
+    RadioGroupContainer::Traverse(mRadioGroupContainer.get(), aCb);
+  }
+}
+
+size_t FragmentOrElement::nsExtendedDOMSlots::SizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+  size_t n =
+      nsIContent::nsExtendedContentSlots::SizeOfExcludingThis(aMallocSizeOf);
+
+  // We own mSMILOverrideStyle but there seems to be no memory reporting on CSS
+  // declarations?  At least report the memory the declaration takes up
+  // directly.
+  if (mSMILOverrideStyle) {
+    n += aMallocSizeOf(mSMILOverrideStyle);
+  }
+
+  // We don't really own mSMILOverrideStyleDeclaration.  mSMILOverrideStyle owns
+  // it.
+
+  // We don't seem to have memory reporting for nsXULControllers.  At least
+  // report the memory it's using directly.
+  if (mControllers) {
+    n += aMallocSizeOf(mControllers);
+  }
+
+  if (mLabelsList) {
+    n += mLabelsList->SizeOfIncludingThis(aMallocSizeOf);
+  }
+
+  // mShadowRoot should be handled during normal DOM tree memory reporting, just
+  // like kids, siblings, etc.
+
+  if (mCustomElementData) {
+    n += mCustomElementData->SizeOfIncludingThis(aMallocSizeOf);
+  }
+
+  if (mRadioGroupContainer) {
+    n += mRadioGroupContainer->SizeOfIncludingThis(aMallocSizeOf);
+  }
+
+  return n;
+}
+
+FragmentOrElement::FragmentOrElement(
+    already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
+    : nsIContent(std::move(aNodeInfo)) {}
+
+FragmentOrElement::~FragmentOrElement() {
+  MOZ_ASSERT(!IsInUncomposedDoc(),
+             "Please remove this from the document properly");
+  if (GetParent()) {
+    NS_RELEASE(mParent);
+  }
+}
+
+static nsINode* FindChromeAccessOnlySubtreeOwner(nsINode* aNode) {
+  if (!aNode->ChromeOnlyAccess()) {
+    return aNode;
+  }
+  return const_cast<nsIContent*>(aNode->GetChromeOnlyAccessSubtreeRootParent());
+}
+
+nsINode* FindChromeAccessOnlySubtreeOwner(EventTarget* aTarget) {
+  nsINode* node = nsINode::FromEventTargetOrNull(aTarget);
+  if (!node) {
+    return nullptr;
+  }
+  return FindChromeAccessOnlySubtreeOwner(node);
+}
+
+void nsIContent::GetEventTargetParent(EventChainPreVisitor& aVisitor) {
+  // FIXME! Document how this event retargeting works, Bug 329124.
+  aVisitor.mCanHandle = true;
+  aVisitor.mMayHaveListenerManager = HasListenerManager();
+
+  if (IsInShadowTree()) {
+    aVisitor.mItemInShadowTree = true;
+  }
+
+  // Don't propagate mouseover and mouseout events when mouse is moving
+  // inside chrome access only content.
+  const bool isAnonForEvents = IsRootOfChromeAccessOnlySubtree();
+  aVisitor.mRootOfClosedTree = isAnonForEvents;
+  if ((aVisitor.mEvent->mMessage == eMouseOver ||
+       aVisitor.mEvent->mMessage == eMouseOut ||
+       aVisitor.mEvent->mMessage == ePointerOver ||
+       aVisitor.mEvent->mMessage == ePointerOut) &&
+      // Check if we should stop event propagation when event has just been
+      // dispatched or when we're about to propagate from
+      // chrome access only subtree or if we are about to propagate out of
+      // a shadow root to a shadow root host.
+      ((this == aVisitor.mEvent->mOriginalTarget && !ChromeOnlyAccess()) ||
+       isAnonForEvents)) {
+    nsIContent* relatedTarget = nsIContent::FromEventTargetOrNull(
+        aVisitor.mEvent->AsMouseEvent()->mRelatedTarget);
+    if (relatedTarget && relatedTarget->OwnerDoc() == OwnerDoc()) {
+      // If current target is anonymous for events or we know that related
+      // target is descendant of an element which is anonymous for events,
+      // we may want to stop event propagation.
+      // If this is the original target, aVisitor.mRelatedTargetIsInAnon
+      // must be updated.
+      if (isAnonForEvents || aVisitor.mRelatedTargetIsInAnon ||
+          (aVisitor.mEvent->mOriginalTarget == this &&
+           (aVisitor.mRelatedTargetIsInAnon =
+                relatedTarget->ChromeOnlyAccess()))) {
+        nsINode* anonOwner = FindChromeAccessOnlySubtreeOwner(this);
+        if (anonOwner) {
+          nsINode* anonOwnerRelated =
+              FindChromeAccessOnlySubtreeOwner(relatedTarget);
+          if (anonOwnerRelated) {
+            // Note, anonOwnerRelated may still be inside some other
+            // native anonymous subtree. The case where anonOwner is still
+            // inside native anonymous subtree will be handled when event
+            // propagates up in the DOM tree.
+            while (anonOwner != anonOwnerRelated &&
+                   anonOwnerRelated->ChromeOnlyAccess()) {
+              anonOwnerRelated =
+                  FindChromeAccessOnlySubtreeOwner(anonOwnerRelated);
+            }
+            if (anonOwner == anonOwnerRelated) {
+#ifdef DEBUG_smaug
+              nsIContent* originalTarget = nsIContent::FromEventTargetOrNull(
+                  aVisitor.mEvent->mOriginalTarget);
+              nsAutoString ot, ct, rt;
+              if (originalTarget) {
+                originalTarget->NodeInfo()->NameAtom()->ToString(ot);
+              }
+              NodeInfo()->NameAtom()->ToString(ct);
+              relatedTarget->NodeInfo()->NameAtom()->ToString(rt);
+              printf(
+                  "Stopping %s propagation:"
+                  "\n\toriginalTarget=%s \n\tcurrentTarget=%s %s"
+                  "\n\trelatedTarget=%s %s \n%s",
+                  (aVisitor.mEvent->mMessage == eMouseOver) ? "mouseover"
+                                                            : "mouseout",
+                  NS_ConvertUTF16toUTF8(ot).get(),
+                  NS_ConvertUTF16toUTF8(ct).get(),
+                  isAnonForEvents
+                      ? "(is native anonymous)"
+                      : (ChromeOnlyAccess() ? "(is in native anonymous subtree)"
+                                            : ""),
+                  NS_ConvertUTF16toUTF8(rt).get(),
+                  relatedTarget->ChromeOnlyAccess()
+                      ? "(is in native anonymous subtree)"
+                      : "",
+                  (originalTarget &&
+                   relatedTarget->FindFirstNonChromeOnlyAccessContent() ==
+                       originalTarget->FindFirstNonChromeOnlyAccessContent())
+                      ? ""
+                      : "Wrong event propagation!?!\n");
+#endif
+              aVisitor.SetParentTarget(nullptr, false);
+              // Event should not propagate to non-anon content.
+              aVisitor.mCanHandle = isAnonForEvents;
+              return;
+            }
+          }
+        }
+      }
+    }
+  }
+
+  // Event parent is the assigned slot, if node is assigned, or node's parent
+  // otherwise.
+  HTMLSlotElement* slot = GetAssignedSlot();
+  nsIContent* parent = slot ? slot : GetParent();
+
+  // Event may need to be retargeted if this is the root of a native anonymous
+  // content subtree.
+  if (isAnonForEvents) {
+#ifdef DEBUG
+    // If a DOM event is explicitly dispatched using node.dispatchEvent(), then
+    // all the events are allowed even in the native anonymous content..
+    nsIContent* t =
+        nsIContent::FromEventTargetOrNull(aVisitor.mEvent->mOriginalTarget);
+    NS_ASSERTION(!t || !t->ChromeOnlyAccess() ||
+                     aVisitor.mEvent->mClass != eMutationEventClass ||
+                     aVisitor.mDOMEvent,
+                 "Mutation event dispatched in native anonymous content!?!");
+#endif
+    if (aVisitor.mEvent->mClass == eTransitionEventClass ||
+        aVisitor.mEvent->mClass == eAnimationEventClass) {
+      // Event should not propagate to non-anon content.
+      aVisitor.SetParentTarget(nullptr, false);
+      return;
+    }
+    aVisitor.mEventTargetAtParent = parent;
+  } else if (parent && aVisitor.mOriginalTargetIsInAnon) {
+    nsIContent* content =
+        nsIContent::FromEventTargetOrNull(aVisitor.mEvent->mTarget);
+    if (content &&
+        content->GetClosestNativeAnonymousSubtreeRootParentOrHost() == parent) {
+      aVisitor.mEventTargetAtParent = parent;
+    }
+  }
+
+  if (!aVisitor.mEvent->mFlags.mComposedInNativeAnonymousContent &&
+      IsRootOfNativeAnonymousSubtree() && OwnerDoc()->GetWindow()) {
+    aVisitor.SetParentTarget(OwnerDoc()->GetWindow()->GetParentTarget(), true);
+  } else if (parent) {
+    aVisitor.SetParentTarget(parent, false);
+    if (slot) {
+      ShadowRoot* root = slot->GetContainingShadow();
+      if (root && root->IsClosed()) {
+        aVisitor.mParentIsSlotInClosedTree = true;
+      }
+    }
+  } else {
+    aVisitor.SetParentTarget(GetComposedDoc(), false);
+  }
+
+  if (!ChromeOnlyAccess() && !aVisitor.mRelatedTargetRetargetedInCurrentScope) {
+    // We don't support Shadow DOM in native anonymous content yet.
+    aVisitor.mRelatedTargetRetargetedInCurrentScope = true;
+    if (aVisitor.mEvent->mOriginalRelatedTarget) {
+      // https://dom.spec.whatwg.org/#concept-event-dispatch
+      // Step 3.
+      // "Let relatedTarget be the result of retargeting event's relatedTarget
+      //  against target if event's relatedTarget is non-null, and null
+      //  otherwise."
+      //
+      // This is a bit complicated because the event might be from native
+      // anonymous content, but we need to deal with non-native anonymous
+      // content there.
+      bool initialTarget = this == aVisitor.mEvent->mOriginalTarget;
+      nsCOMPtr<nsINode> originalTargetAsNode;
+      // Use of mOriginalTargetIsInAnon is an optimization here.
+      if (!initialTarget && aVisitor.mOriginalTargetIsInAnon) {
+        originalTargetAsNode =
+            FindChromeAccessOnlySubtreeOwner(aVisitor.mEvent->mOriginalTarget);
+        initialTarget = originalTargetAsNode == this;
+      }
+      if (initialTarget) {
+        nsCOMPtr<nsINode> relatedTargetAsNode =
+            FindChromeAccessOnlySubtreeOwner(
+                aVisitor.mEvent->mOriginalRelatedTarget);
+        if (!originalTargetAsNode) {
+          originalTargetAsNode =
+              nsINode::FromEventTargetOrNull(aVisitor.mEvent->mOriginalTarget);
+        }
+
+        if (relatedTargetAsNode && originalTargetAsNode) {
+          nsINode* retargetedRelatedTarget = nsContentUtils::Retarget(
+              relatedTargetAsNode, originalTargetAsNode);
+          if (originalTargetAsNode == retargetedRelatedTarget &&
+              retargetedRelatedTarget != relatedTargetAsNode) {
+            // Step 4.
+            // "If target is relatedTarget and target is not event's
+            //  relatedTarget, then return true."
+            aVisitor.IgnoreCurrentTargetBecauseOfShadowDOMRetargeting();
+            // Old code relies on mTarget to point to the first element which
+            // was not added to the event target chain because of mCanHandle
+            // being false, but in Shadow DOM case mTarget really should
+            // point to a node in Shadow DOM.
+            aVisitor.mEvent->mTarget = aVisitor.mTargetInKnownToBeHandledScope;
+            return;
+          }
+
+          // Part of step 5. Retargeting target has happened already higher
+          // up in this method.
+          // "Append to an event path with event, target, targetOverride,
+          //  relatedTarget, and false."
+          aVisitor.mRetargetedRelatedTarget = retargetedRelatedTarget;
+        }
+      } else {
+        nsCOMPtr<nsINode> relatedTargetAsNode =
+            FindChromeAccessOnlySubtreeOwner(
+                aVisitor.mEvent->mOriginalRelatedTarget);
+        if (relatedTargetAsNode) {
+          // Step 11.3.
+          // "Let relatedTarget be the result of retargeting event's
+          // relatedTarget against parent if event's relatedTarget is non-null,
+          // and null otherwise.".
+          nsINode* retargetedRelatedTarget =
+              nsContentUtils::Retarget(relatedTargetAsNode, this);
+          nsCOMPtr<nsINode> targetInKnownToBeHandledScope =
+              FindChromeAccessOnlySubtreeOwner(
+                  aVisitor.mTargetInKnownToBeHandledScope);
+          // If aVisitor.mTargetInKnownToBeHandledScope wasn't nsINode,
+          // targetInKnownToBeHandledScope will be null. This may happen when
+          // dispatching event to Window object in a content page and
+          // propagating the event to a chrome Element.
+          if (targetInKnownToBeHandledScope &&
+              IsShadowIncludingInclusiveDescendantOf(
+                  targetInKnownToBeHandledScope->SubtreeRoot())) {
+            // Part of step 11.4.
+            // "If target's root is a shadow-including inclusive ancestor of
+            //  parent, then"
+            // "...Append to an event path with event, parent, null,
+            // relatedTarget, "   and slot-in-closed-tree."
+            aVisitor.mRetargetedRelatedTarget = retargetedRelatedTarget;
+          } else if (this == retargetedRelatedTarget) {
+            // Step 11.5
+            // "Otherwise, if parent and relatedTarget are identical, then set
+            //  parent to null."
+            aVisitor.IgnoreCurrentTargetBecauseOfShadowDOMRetargeting();
+            // Old code relies on mTarget to point to the first element which
+            // was not added to the event target chain because of mCanHandle
+            // being false, but in Shadow DOM case mTarget really should
+            // point to a node in Shadow DOM.
+            aVisitor.mEvent->mTarget = aVisitor.mTargetInKnownToBeHandledScope;
+            return;
+          } else if (targetInKnownToBeHandledScope) {
+            // Note, if targetInKnownToBeHandledScope is null,
+            // mTargetInKnownToBeHandledScope could be Window object in content
+            // page and we're in chrome document in the same process.
+
+            // Step 11.6
+            aVisitor.mRetargetedRelatedTarget = retargetedRelatedTarget;
+          }
+        }
+      }
+    }
+
+    if (aVisitor.mEvent->mClass == eTouchEventClass) {
+      // Retarget touch objects.
+      MOZ_ASSERT(!aVisitor.mRetargetedTouchTargets.isSome());
+      aVisitor.mRetargetedTouchTargets.emplace();
+      WidgetTouchEvent* touchEvent = aVisitor.mEvent->AsTouchEvent();
+      WidgetTouchEvent::TouchArray& touches = touchEvent->mTouches;
+      for (uint32_t i = 0; i < touches.Length(); ++i) {
+        Touch* touch = touches[i];
+        EventTarget* originalTarget = touch->mOriginalTarget;
+        EventTarget* touchTarget = originalTarget;
+        nsCOMPtr<nsINode> targetAsNode =
+            nsINode::FromEventTargetOrNull(originalTarget);
+        if (targetAsNode) {
+          EventTarget* retargeted =
+              nsContentUtils::Retarget(targetAsNode, this);
+          if (retargeted) {
+            touchTarget = retargeted;
+          }
+        }
+        aVisitor.mRetargetedTouchTargets->AppendElement(touchTarget);
+        touch->mTarget = touchTarget;
+      }
+      MOZ_ASSERT(aVisitor.mRetargetedTouchTargets->Length() ==
+                 touches.Length());
+    }
+  }
+
+  if (slot) {
+    // Inform that we're about to exit the current scope.
+    aVisitor.mRelatedTargetRetargetedInCurrentScope = false;
+  }
+}
+
+Element* nsIContent::GetAutofocusDelegate(bool aWithMouse) const {
+  for (nsINode* node = GetFirstChild(); node; node = node->GetNextNode(this)) {
+    auto* descendant = Element::FromNode(*node);
+    if (!descendant || !descendant->GetBoolAttr(nsGkAtoms::autofocus)) {
+      continue;
+    }
+
+    nsIFrame* frame = descendant->GetPrimaryFrame();
+    if (frame && frame->IsFocusable(aWithMouse)) {
+      return descendant;
+    }
+  }
+  return nullptr;
+}
+
+Element* nsIContent::GetFocusDelegate(bool aWithMouse) const {
+  const nsIContent* whereToLook = this;
+  if (ShadowRoot* root = GetShadowRoot()) {
+    if (!root->DelegatesFocus()) {
+      // 1. If focusTarget is a shadow host and its shadow root 's delegates
+      // focus is false, then return null.
+      return nullptr;
+    }
+    whereToLook = root;
+  }
+
+  auto IsFocusable = [&](Element* aElement) -> Focusable {
+    nsIFrame* frame = aElement->GetPrimaryFrame();
+
+    if (!frame) {
+      return {};
+    }
+
+    return frame->IsFocusable(aWithMouse);
+  };
+
+  Element* potentialFocus = nullptr;
+  for (nsINode* node = whereToLook->GetFirstChild(); node;
+       node = node->GetNextNode(whereToLook)) {
+    auto* el = Element::FromNode(*node);
+    if (!el) {
+      continue;
+    }
+
+    const bool autofocus = el->GetBoolAttr(nsGkAtoms::autofocus);
+
+    if (autofocus) {
+      if (IsFocusable(el)) {
+        // Found an autofocus candidate.
+        return el;
+      }
+    } else if (!potentialFocus) {
+      if (Focusable focusable = IsFocusable(el)) {
+        if (IsHTMLElement(nsGkAtoms::dialog)) {
+          if (focusable.mTabIndex >= 0) {
+            // If focusTarget is a dialog element and descendant is sequentially
+            // focusable, then set focusableArea to descendant.
+            potentialFocus = el;
+          }
+        } else {
+          // This element could be the one if we can't find an
+          // autofocus candidate which has the precedence.
+          potentialFocus = el;
+        }
+      }
+    }
+
+    if (!autofocus && potentialFocus) {
+      // Nothing else to do, we are not looking for more focusable elements
+      // here.
+      continue;
+    }
+
+    if (auto* shadow = el->GetShadowRoot()) {
+      if (shadow->DelegatesFocus()) {
+        if (Element* delegatedFocus = shadow->GetFocusDelegate(aWithMouse)) {
+          if (autofocus) {
+            // This element has autofocus and we found an focus delegates
+            // in its descendants, so use the focus delegates
+            return delegatedFocus;
+          }
+          if (!potentialFocus) {
+            potentialFocus = delegatedFocus;
+          }
+        }
+      }
+    }
+  }
+
+  return potentialFocus;
+}
+
+Focusable nsIContent::IsFocusableWithoutStyle(bool aWithMouse) {
+  // Default, not tabbable
+  return {};
+}
+
+void nsIContent::SetAssignedSlot(HTMLSlotElement* aSlot) {
+  MOZ_ASSERT(aSlot || GetExistingExtendedContentSlots());
+  ExtendedContentSlots()->mAssignedSlot = aSlot;
+}
+
+#ifdef MOZ_DOM_LIST
+void nsIContent::Dump() { List(); }
+#endif
+
+void FragmentOrElement::GetTextContentInternal(nsAString& aTextContent,
+                                               OOMReporter& aError) {
+  if (!nsContentUtils::GetNodeTextContent(this, true, aTextContent, fallible)) {
+    aError.ReportOOM();
+  }
+}
+
+void FragmentOrElement::SetTextContentInternal(const nsAString& aTextContent,
+                                               nsIPrincipal* aSubjectPrincipal,
+                                               ErrorResult& aError) {
+  bool tryReuse = false;
+  if (!aTextContent.IsEmpty()) {
+    if (nsIContent* firstChild = GetFirstChild()) {
+      tryReuse = firstChild->NodeType() == TEXT_NODE &&
+                 !firstChild->GetNextSibling() &&
+                 firstChild->OwnedOnlyByTheDOMAndFrameTrees() &&
+#ifdef ACCESSIBILITY
+                 !GetAccService() &&
+#endif
+                 !OwnerDoc()->MayHaveDOMMutationObservers() &&
+                 !nsContentUtils::HasMutationListeners(
+                     OwnerDoc(), NS_EVENT_BITS_MUTATION_ALL);
+    }
+  }
+
+  aError = nsContentUtils::SetNodeTextContent(this, aTextContent, tryReuse);
+}
+
+void FragmentOrElement::DestroyContent() {
+  // Drop any servo data. We do this before the RemovedFromDocument call below
+  // so that it doesn't need to try to keep the style state sane when shuffling
+  // around the flattened tree.
+  //
+  // TODO(emilio): I suspect this can be asserted against instead, with a bit of
+  // effort to avoid calling Document::Destroy with a shell...
+  if (IsElement()) {
+    AsElement()->ClearServoData();
+  }
+
+#ifdef DEBUG
+  uint32_t oldChildCount = GetChildCount();
+#endif
+
+  for (nsIContent* child = GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    child->DestroyContent();
+    MOZ_ASSERT(child->GetParent() == this,
+               "Mutating the tree during XBL destructors is evil");
+  }
+
+  MOZ_ASSERT(oldChildCount == GetChildCount(),
+             "Mutating the tree during XBL destructors is evil");
+
+  if (ShadowRoot* shadowRoot = GetShadowRoot()) {
+    shadowRoot->DestroyContent();
+  }
+}
+
+void FragmentOrElement::SaveSubtreeState() {
+  for (nsIContent* child = GetFirstChild(); child;
+       child = child->GetNextSibling()) {
+    child->SaveSubtreeState();
+  }
+
+  // FIXME(bug 1469277): Pretty sure this wants to dig into shadow trees as
+  // well.
+}
+
+//----------------------------------------------------------------------
+
+// Generic DOMNode implementations
+
+void FragmentOrElement::FireNodeInserted(
+    Document* aDoc, nsINode* aParent,
+    const nsTArray<nsCOMPtr<nsIContent>>& aNodes) {
+  for (const nsCOMPtr<nsIContent>& childContent : aNodes) {
+    if (nsContentUtils::HasMutationListeners(
+            childContent, NS_EVENT_BITS_MUTATION_NODEINSERTED, aParent)) {
+      InternalMutationEvent mutation(true, eLegacyNodeInserted);
+      mutation.mRelatedNode = aParent;
+
+      mozAutoSubtreeModified subtree(aDoc, aParent);
+      AsyncEventDispatcher::RunDOMEventWhenSafe(*childContent, mutation);
+    }
+  }
+}
+
+//----------------------------------------------------------------------
+
+// nsISupports implementation
+
+#define SUBTREE_UNBINDINGS_PER_RUNNABLE 500
+
+class ContentUnbinder : public Runnable {
+ public:
+  ContentUnbinder() : Runnable("ContentUnbinder") { mLast = this; }
+
+  ~ContentUnbinder() { Run(); }
+
+  void UnbindSubtree(nsIContent* aNode) {
+    if (aNode->NodeType() != nsINode::ELEMENT_NODE &&
+        aNode->NodeType() != nsINode::DOCUMENT_FRAGMENT_NODE) {
+      return;
+    }
+    FragmentOrElement* container = static_cast<FragmentOrElement*>(aNode);
+    if (container->HasChildren()) {
+      // Invalidate cached array of child nodes
+      container->InvalidateChildNodes();
+
+      while (container->HasChildren()) {
+        // Hold a strong ref to the node when we remove it, because we may be
+        // the last reference to it.  We need to call DisconnectChild()
+        // before calling UnbindFromTree, since this last can notify various
+        // observers and they should really see consistent
+        // tree state.
+        // If this code changes, change the corresponding code in
+        // FragmentOrElement's and Document's unlink impls.
+        nsCOMPtr<nsIContent> child = container->GetLastChild();
+        container->DisconnectChild(child);
+        UnbindSubtree(child);
+        child->UnbindFromTree();
+      }
+    }
+  }
+
+  NS_IMETHOD Run() override {
+    nsAutoScriptBlocker scriptBlocker;
+    uint32_t len = mSubtreeRoots.Length();
+    if (len) {
+      for (uint32_t i = 0; i < len; ++i) {
+        UnbindSubtree(mSubtreeRoots[i]);
+      }
+      mSubtreeRoots.Clear();
+    }
+    nsCycleCollector_dispatchDeferredDeletion();
+    if (this == sContentUnbinder) {
+      sContentUnbinder = nullptr;
+      if (mNext) {
+        RefPtr<ContentUnbinder> next;
+        next.swap(mNext);
+        sContentUnbinder = next;
+        next->mLast = mLast;
+        mLast = nullptr;
+        NS_DispatchToCurrentThreadQueue(next.forget(),
+                                        EventQueuePriority::Idle);
+      }
+    }
+    return NS_OK;
+  }
+
+  static void UnbindAll() {
+    RefPtr<ContentUnbinder> ub = sContentUnbinder;
+    sContentUnbinder = nullptr;
+    while (ub) {
+      ub->Run();
+      ub = ub->mNext;
+    }
+  }
+
+  static void Append(nsIContent* aSubtreeRoot) {
+    if (!sContentUnbinder) {
+      sContentUnbinder = new ContentUnbinder();
+      nsCOMPtr<nsIRunnable> e = sContentUnbinder;
+      NS_DispatchToCurrentThreadQueue(e.forget(), EventQueuePriority::Idle);
+    }
+
+    if (sContentUnbinder->mLast->mSubtreeRoots.Length() >=
+        SUBTREE_UNBINDINGS_PER_RUNNABLE) {
+      sContentUnbinder->mLast->mNext = new ContentUnbinder();
+      sContentUnbinder->mLast = sContentUnbinder->mLast->mNext;
+    }
+    sContentUnbinder->mLast->mSubtreeRoots.AppendElement(aSubtreeRoot);
+  }
+
+ private:
+  AutoTArray<nsCOMPtr<nsIContent>, SUBTREE_UNBINDINGS_PER_RUNNABLE>
+      mSubtreeRoots;
+  RefPtr<ContentUnbinder> mNext;
+  ContentUnbinder* mLast;
+  static ContentUnbinder* sContentUnbinder;
+};
+
+ContentUnbinder* ContentUnbinder::sContentUnbinder = nullptr;
+
+void FragmentOrElement::ClearContentUnbinder() { ContentUnbinder::UnbindAll(); }
+
+// Note, _INHERITED macro isn't used here since nsINode implementations are
+// rather special.
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(FragmentOrElement)
+
+// We purposefully don't UNLINK_BEGIN_INHERITED here.
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(FragmentOrElement)
+  nsIContent::Unlink(tmp);
+
+  if (tmp->HasProperties()) {
+    if (tmp->IsElement()) {
+      Element* elem = tmp->AsElement();
+      elem->UnlinkIntersectionObservers();
+    }
+
+    if (tmp->IsHTMLElement() || tmp->IsSVGElement()) {
+      nsStaticAtom* const* props =
+          Element::HTMLSVGPropertiesToTraverseAndUnlink();
+      for (uint32_t i = 0; props[i]; ++i) {
+        tmp->RemoveProperty(props[i]);
+      }
+    }
+  }
+
+  // Unlink child content (and unbind our subtree).
+  if (tmp->UnoptimizableCCNode() || !nsCCUncollectableMarker::sGeneration) {
+    // Don't allow script to run while we're unbinding everything.
+    nsAutoScriptBlocker scriptBlocker;
+    while (tmp->HasChildren()) {
+      // Hold a strong ref to the node when we remove it, because we may be
+      // the last reference to it.
+      // If this code changes, change the corresponding code in Document's
+      // unlink impl and ContentUnbinder::UnbindSubtree.
+      nsCOMPtr<nsIContent> child = tmp->GetLastChild();
+      tmp->DisconnectChild(child);
+      child->UnbindFromTree();
+    }
+  } else if (!tmp->GetParent() && tmp->HasChildren()) {
+    ContentUnbinder::Append(tmp);
+  } /* else {
+    The subtree root will end up to a ContentUnbinder, and that will
+    unbind the child nodes.
+  } */
+
+  if (ShadowRoot* shadowRoot = tmp->GetShadowRoot()) {
+    shadowRoot->Unbind();
+    tmp->ExtendedDOMSlots()->mShadowRoot = nullptr;
+  }
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+void FragmentOrElement::MarkNodeChildren(nsINode* aNode) {
+  JSObject* o = GetJSObjectChild(aNode);
+  if (o) {
+    JS::ExposeObjectToActiveJS(o);
+  }
+
+  EventListenerManager* elm = aNode->GetExistingListenerManager();
+  if (elm) {
+    elm->MarkForCC();
+  }
+}
+
+nsINode* FindOptimizableSubtreeRoot(nsINode* aNode) {
+  nsINode* p;
+  while ((p = aNode->GetParentNode())) {
+    if (aNode->UnoptimizableCCNode()) {
+      return nullptr;
+    }
+    aNode = p;
+  }
+
+  if (aNode->UnoptimizableCCNode()) {
+    return nullptr;
+  }
+  return aNode;
+}
+
+StaticAutoPtr<nsTHashSet<nsINode*>> gCCBlackMarkedNodes;
+
+static void ClearBlackMarkedNodes() {
+  if (!gCCBlackMarkedNodes) {
+    return;
+  }
+  for (nsINode* n : *gCCBlackMarkedNodes) {
+    n->SetCCMarkedRoot(false);
+    n->SetInCCBlackTree(false);
+  }
+  gCCBlackMarkedNodes = nullptr;
+}
+
+// static
+void FragmentOrElement::RemoveBlackMarkedNode(nsINode* aNode) {
+  if (!gCCBlackMarkedNodes) {
+    return;
+  }
+  gCCBlackMarkedNodes->Remove(aNode);
+}
+
+static bool IsCertainlyAliveNode(nsINode* aNode, Document* aDoc) {
+  MOZ_ASSERT(aNode->GetComposedDoc() == aDoc);
+
+  // Marked to be in-CC-generation or if the document is an svg image that's
+  // being kept alive by the image cache. (Note that an svg image's internal
+  // SVG document will receive an OnPageHide() call when it gets purged from
+  // the image cache; hence, we use IsVisible() as a hint that the document is
+  // actively being kept alive by the cache.)
+  return nsCCUncollectableMarker::InGeneration(aDoc->GetMarkedCCGeneration()) ||
+         (nsCCUncollectableMarker::sGeneration && aDoc->IsBeingUsedAsImage() &&
+          aDoc->IsVisible());
+}
+
+// static
+bool FragmentOrElement::CanSkipInCC(nsINode* aNode) {
+  // Don't try to optimize anything during shutdown.
+  if (nsCCUncollectableMarker::sGeneration == 0) {
+    return false;
+  }
+
+  Document* currentDoc = aNode->GetComposedDoc();
+  if (currentDoc && IsCertainlyAliveNode(aNode, currentDoc)) {
+    return !NeedsScriptTraverse(aNode);
+  }
+
+  // Bail out early if aNode is somewhere in anonymous content,
+  // or otherwise unusual.
+  if (aNode->UnoptimizableCCNode()) {
+    return false;
+  }
+
+  nsINode* root = currentDoc ? static_cast<nsINode*>(currentDoc)
+                             : FindOptimizableSubtreeRoot(aNode);
+  if (!root) {
+    return false;
+  }
+
+  // Subtree has been traversed already.
+  if (root->CCMarkedRoot()) {
+    return root->InCCBlackTree() && !NeedsScriptTraverse(aNode);
+  }
+
+  if (!gCCBlackMarkedNodes) {
+    gCCBlackMarkedNodes = new nsTHashSet<nsINode*>(1020);
+  }
+
+  // nodesToUnpurple contains nodes which will be removed
+  // from the purple buffer if the DOM tree is known-live.
+  AutoTArray<nsIContent*, 1020> nodesToUnpurple;
+  // grayNodes need script traverse, so they aren't removed from
+  // the purple buffer, but are marked to be in known-live subtree so that
+  // traverse is faster.
+  AutoTArray<nsINode*, 1020> grayNodes;
+
+  bool foundLiveWrapper = root->HasKnownLiveWrapper();
+  if (root != currentDoc) {
+    currentDoc = nullptr;
+    if (NeedsScriptTraverse(root)) {
+      grayNodes.AppendElement(root);
+    } else if (static_cast<nsIContent*>(root)->IsPurple()) {
+      nodesToUnpurple.AppendElement(static_cast<nsIContent*>(root));
+    }
+  }
+
+  // Traverse the subtree and check if we could know without CC
+  // that it is known-live.
+  // Note, this traverse is non-virtual and inline, so it should be a lot faster
+  // than CC's generic traverse.
+  for (nsIContent* node = root->GetFirstChild(); node;
+       node = node->GetNextNode(root)) {
+    foundLiveWrapper = foundLiveWrapper || node->HasKnownLiveWrapper();
+    if (foundLiveWrapper && currentDoc) {
+      // If we can mark the whole document known-live, no need to optimize
+      // so much, since when the next purple node in the document will be
+      // handled, it is fast to check that currentDoc is in CCGeneration.
+      break;
+    }
+    if (NeedsScriptTraverse(node)) {
+      // Gray nodes need real CC traverse.
+      grayNodes.AppendElement(node);
+    } else if (node->IsPurple()) {
+      nodesToUnpurple.AppendElement(node);
+    }
+  }
+
+  root->SetCCMarkedRoot(true);
+  root->SetInCCBlackTree(foundLiveWrapper);
+  gCCBlackMarkedNodes->Insert(root);
+
+  if (!foundLiveWrapper) {
+    return false;
+  }
+
+  if (currentDoc) {
+    // Special case documents. If we know the document is known-live,
+    // we can mark the document to be in CCGeneration.
+    currentDoc->MarkUncollectableForCCGeneration(
+        nsCCUncollectableMarker::sGeneration);
+  } else {
+    for (uint32_t i = 0; i < grayNodes.Length(); ++i) {
+      nsINode* node = grayNodes[i];
+      node->SetInCCBlackTree(true);
+      gCCBlackMarkedNodes->Insert(node);
+    }
+  }
+
+  // Subtree is known-live, we can remove non-gray purple nodes from
+  // purple buffer.
+  for (uint32_t i = 0; i < nodesToUnpurple.Length(); ++i) {
+    nsIContent* purple = nodesToUnpurple[i];
+    // Can't remove currently handled purple node.
+    if (purple != aNode) {
+      purple->RemovePurple();
+    }
+  }
+  return !NeedsScriptTraverse(aNode);
+}
+
+AutoTArray<nsINode*, 1020>* gPurpleRoots = nullptr;
+AutoTArray<nsIContent*, 1020>* gNodesToUnbind = nullptr;
+
+void ClearCycleCollectorCleanupData() {
+  if (gPurpleRoots) {
+    uint32_t len = gPurpleRoots->Length();
+    for (uint32_t i = 0; i < len; ++i) {
+      nsINode* n = gPurpleRoots->ElementAt(i);
+      n->SetIsPurpleRoot(false);
+    }
+    delete gPurpleRoots;
+    gPurpleRoots = nullptr;
+  }
+  if (gNodesToUnbind) {
+    uint32_t len = gNodesToUnbind->Length();
+    for (uint32_t i = 0; i < len; ++i) {
+      nsIContent* c = gNodesToUnbind->ElementAt(i);
+      c->SetIsPurpleRoot(false);
+      ContentUnbinder::Append(c);
+    }
+    delete gNodesToUnbind;
+    gNodesToUnbind = nullptr;
+  }
+}
+
+static bool ShouldClearPurple(nsIContent* aContent) {
+  MOZ_ASSERT(aContent);
+  if (aContent->IsPurple()) {
+    return true;
+  }
+
+  JSObject* o = GetJSObjectChild(aContent);
+  if (o && JS::ObjectIsMarkedGray(o)) {
+    return true;
+  }
+
+  if (aContent->HasListenerManager()) {
+    return true;
+  }
+
+  return aContent->HasProperties();
+}
+
+// If aNode is not optimizable, but is an element
+// with a frame in a document which has currently active presshell,
+// we can act as if it was optimizable. When the primary frame dies, aNode
+// will end up to the purple buffer because of the refcount change.
+bool NodeHasActiveFrame(Document* aCurrentDoc, nsINode* aNode) {
+  return aCurrentDoc->GetPresShell() && aNode->IsElement() &&
+         aNode->AsElement()->GetPrimaryFrame();
+}
+
+// CanSkip checks if aNode is known-live, and if it is, returns true. If aNode
+// is in a known-live DOM tree, CanSkip may also remove other objects from
+// purple buffer and unmark event listeners and user data.  If the root of the
+// DOM tree is a document, less optimizations are done since checking the
+// liveness of the current document is usually fast and we don't want slow down
+// such common cases.
+bool FragmentOrElement::CanSkip(nsINode* aNode, bool aRemovingAllowed) {
+  // Don't try to optimize anything during shutdown.
+  if (nsCCUncollectableMarker::sGeneration == 0) {
+    return false;
+  }
+
+  bool unoptimizable = aNode->UnoptimizableCCNode();
+  Document* currentDoc = aNode->GetComposedDoc();
+  if (currentDoc && IsCertainlyAliveNode(aNode, currentDoc) &&
+      (!unoptimizable || NodeHasActiveFrame(currentDoc, aNode))) {
+    MarkNodeChildren(aNode);
+    return true;
+  }
+
+  if (unoptimizable) {
+    return false;
+  }
+
+  nsINode* root = currentDoc ? static_cast<nsINode*>(currentDoc)
+                             : FindOptimizableSubtreeRoot(aNode);
+  if (!root) {
+    return false;
+  }
+
+  // Subtree has been traversed already, and aNode has
+  // been handled in a way that doesn't require revisiting it.
+  if (root->IsPurpleRoot()) {
+    return false;
+  }
+
+  // nodesToClear contains nodes which are either purple or
+  // gray.
+  AutoTArray<nsIContent*, 1020> nodesToClear;
+
+  bool foundLiveWrapper = root->HasKnownLiveWrapper();
+  bool domOnlyCycle = false;
+  if (root != currentDoc) {
+    currentDoc = nullptr;
+    if (!foundLiveWrapper) {
+      domOnlyCycle = static_cast<nsIContent*>(root)->OwnedOnlyByTheDOMTree();
+    }
+    if (ShouldClearPurple(static_cast<nsIContent*>(root))) {
+      nodesToClear.AppendElement(static_cast<nsIContent*>(root));
+    }
+  }
+
+  // Traverse the subtree and check if we could know without CC
+  // that it is known-live.
+  // Note, this traverse is non-virtual and inline, so it should be a lot faster
+  // than CC's generic traverse.
+  for (nsIContent* node = root->GetFirstChild(); node;
+       node = node->GetNextNode(root)) {
+    foundLiveWrapper = foundLiveWrapper || node->HasKnownLiveWrapper();
+    if (foundLiveWrapper) {
+      domOnlyCycle = false;
+      if (currentDoc) {
+        // If we can mark the whole document live, no need to optimize
+        // so much, since when the next purple node in the document will be
+        // handled, it is fast to check that the currentDoc is in CCGeneration.
+        break;
+      }
+      // No need to put stuff to the nodesToClear array, if we can clear it
+      // already here.
+      if (node->IsPurple() && (node != aNode || aRemovingAllowed)) {
+        node->RemovePurple();
+      }
+      MarkNodeChildren(node);
+    } else {
+      domOnlyCycle = domOnlyCycle && node->OwnedOnlyByTheDOMTree();
+      if (ShouldClearPurple(node)) {
+        // Collect interesting nodes which we can clear if we find that
+        // they are kept alive in a known-live tree or are in a DOM-only cycle.
+        nodesToClear.AppendElement(node);
+      }
+    }
+  }
+
+  if (!currentDoc || !foundLiveWrapper) {
+    root->SetIsPurpleRoot(true);
+    if (domOnlyCycle) {
+      if (!gNodesToUnbind) {
+        gNodesToUnbind = new AutoTArray<nsIContent*, 1020>();
+      }
+      gNodesToUnbind->AppendElement(static_cast<nsIContent*>(root));
+      for (uint32_t i = 0; i < nodesToClear.Length(); ++i) {
+        nsIContent* n = nodesToClear[i];
+        if ((n != aNode || aRemovingAllowed) && n->IsPurple()) {
+          n->RemovePurple();
+        }
+      }
+      return true;
+    } else {
+      if (!gPurpleRoots) {
+        gPurpleRoots = new AutoTArray<nsINode*, 1020>();
+      }
+      gPurpleRoots->AppendElement(root);
+    }
+  }
+
+  if (!foundLiveWrapper) {
+    return false;
+  }
+
+  if (currentDoc) {
+    // Special case documents. If we know the document is known-live,
+    // we can mark the document to be in CCGeneration.
+    currentDoc->MarkUncollectableForCCGeneration(
+        nsCCUncollectableMarker::sGeneration);
+    MarkNodeChildren(currentDoc);
+  }
+
+  // Subtree is known-live, so we can remove purple nodes from
+  // purple buffer and mark stuff that to be certainly alive.
+  for (uint32_t i = 0; i < nodesToClear.Length(); ++i) {
+    nsIContent* n = nodesToClear[i];
+    MarkNodeChildren(n);
+    // Can't remove currently handled purple node,
+    // unless aRemovingAllowed is true.
+    if ((n != aNode || aRemovingAllowed) && n->IsPurple()) {
+      n->RemovePurple();
+    }
+  }
+  return true;
+}
+
+bool FragmentOrElement::CanSkipThis(nsINode* aNode) {
+  if (nsCCUncollectableMarker::sGeneration == 0) {
+    return false;
+  }
+  if (aNode->HasKnownLiveWrapper()) {
+    return true;
+  }
+  Document* c = aNode->GetComposedDoc();
+  return ((c && IsCertainlyAliveNode(aNode, c)) || aNode->InCCBlackTree()) &&
+         !NeedsScriptTraverse(aNode);
+}
+
+void FragmentOrElement::InitCCCallbacks() {
+  nsCycleCollector_setForgetSkippableCallback(ClearCycleCollectorCleanupData);
+  nsCycleCollector_setBeforeUnlinkCallback(ClearBlackMarkedNodes);
+}
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(FragmentOrElement)
+  return FragmentOrElement::CanSkip(tmp, aRemovingAllowed);
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(FragmentOrElement)
+  return FragmentOrElement::CanSkipInCC(tmp);
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END
+
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(FragmentOrElement)
+  return FragmentOrElement::CanSkipThis(tmp);
+NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END
+
+// We purposefully don't TRAVERSE_BEGIN_INHERITED here.  All the bits
+// we should traverse should be added here or in nsINode::Traverse.
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(FragmentOrElement)
+  if (MOZ_UNLIKELY(cb.WantDebugInfo())) {
+    char name[512];
+    uint32_t nsid = tmp->GetNameSpaceID();
+    nsAtomCString localName(tmp->NodeInfo()->NameAtom());
+    nsAutoCString uri;
+    if (tmp->OwnerDoc()->GetDocumentURI()) {
+      uri = tmp->OwnerDoc()->GetDocumentURI()->GetSpecOrDefault();
+    }
+
+    nsAutoString id;
+    nsAtom* idAtom = tmp->GetID();
+    if (idAtom) {
+      id.AppendLiteral(" id='");
+      id.Append(nsDependentAtomString(idAtom));
+      id.Append('\'');
+    }
+
+    nsAutoString classes;
+    const nsAttrValue* classAttrValue =
+        tmp->IsElement() ? tmp->AsElement()->GetClasses() : nullptr;
+    if (classAttrValue) {
+      classes.AppendLiteral(" class='");
+      nsAutoString classString;
+      classAttrValue->ToString(classString);
+      classString.ReplaceChar(char16_t('\n'), char16_t(' '));
+      classes.Append(classString);
+      classes.Append('\'');
+    }
+
+    nsAutoCString orphan;
+    if (!tmp->IsInComposedDoc()) {
+      orphan.AppendLiteral(" (orphan)");
+    }
+
+    const char* nsuri = nsNameSpaceManager::GetNameSpaceDisplayName(nsid);
+    SprintfLiteral(name, "FragmentOrElement %s %s%s%s%s %s", nsuri,
+                   localName.get(), NS_ConvertUTF16toUTF8(id).get(),
+                   NS_ConvertUTF16toUTF8(classes).get(), orphan.get(),
+                   uri.get());
+    cb.DescribeRefCountedNode(tmp->mRefCnt.get(), name);
+  } else {
+    NS_IMPL_CYCLE_COLLECTION_DESCRIBE(FragmentOrElement, tmp->mRefCnt.get())
+  }
+
+  if (!nsIContent::Traverse(tmp, cb)) {
+    return NS_SUCCESS_INTERRUPTED_TRAVERSE;
+  }
+
+  if (tmp->HasProperties()) {
+    if (tmp->IsElement()) {
+      Element* elem = tmp->AsElement();
+      IntersectionObserverList* observers =
+          static_cast<IntersectionObserverList*>(
+              elem->GetProperty(nsGkAtoms::intersectionobserverlist));
+      if (observers) {
+        for (DOMIntersectionObserver* observer : observers->Keys()) {
+          cb.NoteXPCOMChild(observer);
+        }
+      }
+    }
+    if (tmp->IsHTMLElement() || tmp->IsSVGElement()) {
+      nsStaticAtom* const* props =
+          Element::HTMLSVGPropertiesToTraverseAndUnlink();
+      for (uint32_t i = 0; props[i]; ++i) {
+        nsISupports* property =
+            static_cast<nsISupports*>(tmp->GetProperty(props[i]));
+        cb.NoteXPCOMChild(property);
+      }
+    }
+  }
+  if (tmp->IsElement()) {
+    Element* element = tmp->AsElement();
+    // Traverse attribute names.
+    uint32_t i;
+    uint32_t attrs = element->GetAttrCount();
+    for (i = 0; i < attrs; i++) {
+      const nsAttrName* name = element->GetUnsafeAttrNameAt(i);
+      if (!name->IsAtom()) {
+        NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(cb, "mAttrs[i]->NodeInfo()");
+        cb.NoteNativeChild(name->NodeInfo(),
+                           NS_CYCLE_COLLECTION_PARTICIPANT(NodeInfo));
+      }
+    }
+  }
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_INTERFACE_MAP_BEGIN(FragmentOrElement)
+  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(FragmentOrElement)
+NS_INTERFACE_MAP_END_INHERITING(nsIContent)
+
+//----------------------------------------------------------------------
+
+const nsTextFragment* FragmentOrElement::GetText() { return nullptr; }
+
+uint32_t FragmentOrElement::TextLength() const {
+  // We can remove this assertion if it turns out to be useful to be able
+  // to depend on this returning 0
+  MOZ_ASSERT_UNREACHABLE("called FragmentOrElement::TextLength");
+
+  return 0;
+}
+
+bool FragmentOrElement::TextIsOnlyWhitespace() { return false; }
+
+bool FragmentOrElement::ThreadSafeTextIsOnlyWhitespace() const { return false; }
+
+static inline bool IsVoidTag(nsAtom* aTag) {
+  static const nsAtom* voidElements[] = {
+      nsGkAtoms::area,    nsGkAtoms::base,  nsGkAtoms::basefont,
+      nsGkAtoms::bgsound, nsGkAtoms::br,    nsGkAtoms::col,
+      nsGkAtoms::embed,   nsGkAtoms::frame, nsGkAtoms::hr,
+      nsGkAtoms::img,     nsGkAtoms::input, nsGkAtoms::keygen,
+      nsGkAtoms::link,    nsGkAtoms::meta,  nsGkAtoms::param,
+      nsGkAtoms::source,  nsGkAtoms::track, nsGkAtoms::wbr};
+
+  static mozilla::BitBloomFilter<12, nsAtom> sFilter;
+  static bool sInitialized = false;
+  if (!sInitialized) {
+    sInitialized = true;
+    for (uint32_t i = 0; i < ArrayLength(voidElements); ++i) {
+      sFilter.add(voidElements[i]);
+    }
+  }
+
+  if (sFilter.mightContain(aTag)) {
+    for (uint32_t i = 0; i < ArrayLength(voidElements); ++i) {
+      if (aTag == voidElements[i]) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+/* static */
+bool FragmentOrElement::IsHTMLVoid(nsAtom* aLocalName) {
+  return aLocalName && IsVoidTag(aLocalName);
+}
+
+void FragmentOrElement::GetMarkup(bool aIncludeSelf, nsAString& aMarkup) {
+  aMarkup.Truncate();
+
+  Document* doc = OwnerDoc();
+  if (IsInHTMLDocument()) {
+    nsContentUtils::SerializeNodeToMarkup(this, !aIncludeSelf, aMarkup);
+    return;
+  }
+
+  nsAutoString contentType;
+  doc->GetContentType(contentType);
+  bool tryToCacheEncoder = !aIncludeSelf;
+
+  nsCOMPtr<nsIDocumentEncoder> docEncoder = doc->GetCachedEncoder();
+  if (!docEncoder) {
+    docEncoder = do_createDocumentEncoder(
+        PromiseFlatCString(NS_ConvertUTF16toUTF8(contentType)).get());
+  }
+  if (!docEncoder) {
+    // This could be some type for which we create a synthetic document.  Try
+    // again as XML
+    contentType.AssignLiteral("application/xml");
+    docEncoder = do_createDocumentEncoder("application/xml");
+    // Don't try to cache the encoder since it would point to a different
+    // contentType once it has been reinitialized.
+    tryToCacheEncoder = false;
+  }
+
+  NS_ENSURE_TRUE_VOID(docEncoder);
+
+  uint32_t flags = nsIDocumentEncoder::OutputEncodeBasicEntities |
+                   // Output DOM-standard newlines
+                   nsIDocumentEncoder::OutputLFLineBreak |
+                   // Don't do linebreaking that's not present in
+                   // the source
+                   nsIDocumentEncoder::OutputRaw |
+                   // Only check for mozdirty when necessary (bug 599983)
+                   nsIDocumentEncoder::OutputIgnoreMozDirty;
+
+  if (IsEditable()) {
+    nsCOMPtr<Element> elem = do_QueryInterface(this);
+    TextEditor* textEditor = elem ? elem->GetTextEditorInternal() : nullptr;
+    if (textEditor && textEditor->OutputsMozDirty()) {
+      flags &= ~nsIDocumentEncoder::OutputIgnoreMozDirty;
+    }
+  }
+
+  DebugOnly<nsresult> rv = docEncoder->NativeInit(doc, contentType, flags);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+
+  if (aIncludeSelf) {
+    docEncoder->SetNode(this);
+  } else {
+    docEncoder->SetContainerNode(this);
+  }
+  rv = docEncoder->EncodeToString(aMarkup);
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  if (tryToCacheEncoder) {
+    doc->SetCachedEncoder(docEncoder.forget());
+  }
+}
+
+static bool ContainsMarkup(const nsAString& aStr) {
+  // Note: we can't use FindCharInSet because null is one of the characters we
+  // want to search for.
+  const char16_t* start = aStr.BeginReading();
+  const char16_t* end = aStr.EndReading();
+
+  while (start != end) {
+    char16_t c = *start;
+    if (c == char16_t('<') || c == char16_t('&') || c == char16_t('\r') ||
+        c == char16_t('\0')) {
+      return true;
+    }
+    ++start;
+  }
+
+  return false;
+}
+
+void FragmentOrElement::SetInnerHTMLInternal(const nsAString& aInnerHTML,
+                                             ErrorResult& aError) {
+  // Keep "this" alive should be guaranteed by the caller, and also the content
+  // of a template element (if this is one) should never been released by from
+  // this during this call.  Therefore, using raw pointer here is safe.
+  FragmentOrElement* target = this;
+  // Handle template case.
+  if (target->IsTemplateElement()) {
+    DocumentFragment* frag =
+        static_cast<HTMLTemplateElement*>(target)->Content();
+    MOZ_ASSERT(frag);
+    target = frag;
+  }
+  // Fast-path for strings with no markup. Limit this to short strings, to
+  // avoid ContainsMarkup taking too long. The choice for 100 is based on
+  // gut feeling.
+  //
+  // Don't do this for elements with a weird parser insertion mode, for
+  // instance setting innerHTML = "" on a <html> element should add the
+  // optional <head> and <body> elements.
+  if (!target->HasWeirdParserInsertionMode() && aInnerHTML.Length() < 100 &&
+      !ContainsMarkup(aInnerHTML)) {
+    aError = nsContentUtils::SetNodeTextContent(target, aInnerHTML, false);
+    return;
+  }
+
+  // mozAutoSubtreeModified keeps the owner document alive.  Therefore, using a
+  // raw pointer here is safe.
+  Document* const doc = target->OwnerDoc();
+
+  // Batch possible DOMSubtreeModified events.
+  mozAutoSubtreeModified subtree(doc, nullptr);
+
+  target->FireNodeRemovedForChildren();
+
+  // Needed when innerHTML is used in combination with contenteditable
+  mozAutoDocUpdate updateBatch(doc, true);
+
+  // Remove childnodes.
+  nsAutoMutationBatch mb(target, true, false);
+  while (target->HasChildren()) {
+    target->RemoveChildNode(target->GetFirstChild(), true);
+  }
+  mb.RemovalDone();
+
+  nsAutoScriptLoaderDisabler sld(doc);
+
+  FragmentOrElement* parseContext = this;
+  if (ShadowRoot* shadowRoot = ShadowRoot::FromNode(this)) {
+    // Fix up the context to be the host of the ShadowRoot.  See
+    // https://w3c.github.io/DOM-Parsing/#dom-innerhtml-innerhtml setter step 1.
+    parseContext = shadowRoot->GetHost();
+  }
+
+  if (doc->IsHTMLDocument()) {
+    nsAtom* contextLocalName = parseContext->NodeInfo()->NameAtom();
+    int32_t contextNameSpaceID = parseContext->GetNameSpaceID();
+
+    int32_t oldChildCount = target->GetChildCount();
+    aError = nsContentUtils::ParseFragmentHTML(
+        aInnerHTML, target, contextLocalName, contextNameSpaceID,
+        doc->GetCompatibilityMode() == eCompatibility_NavQuirks, true);
+    mb.NodesAdded();
+    // HTML5 parser has notified, but not fired mutation events.
+    nsContentUtils::FireMutationEventsForDirectParsing(doc, target,
+                                                       oldChildCount);
+  } else {
+    RefPtr<DocumentFragment> df = nsContentUtils::CreateContextualFragment(
+        parseContext, aInnerHTML, true, aError);
+    if (!aError.Failed()) {
+      // Suppress assertion about node removal mutation events that can't have
+      // listeners anyway, because no one has had the chance to register
+      // mutation listeners on the fragment that comes from the parser.
+      nsAutoScriptBlockerSuppressNodeRemoved scriptBlocker;
+
+      target->AppendChild(*df, aError);
+      mb.NodesAdded();
+    }
+  }
+}
+
+void FragmentOrElement::AddSizeOfExcludingThis(nsWindowSizes& aSizes,
+                                               size_t* aNodeSize) const {
+  nsIContent::AddSizeOfExcludingThis(aSizes, aNodeSize);
+
+  nsDOMSlots* slots = GetExistingDOMSlots();
+  if (slots) {
+    *aNodeSize += slots->SizeOfIncludingThis(aSizes.mState.mMallocSizeOf);
+  }
+}