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diff --git a/layout/base/RestyleManager.h b/layout/base/RestyleManager.h
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+/* -*- 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/. */
+
+#ifndef mozilla_RestyleManager_h
+#define mozilla_RestyleManager_h
+
+#include "mozilla/AutoRestore.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/OverflowChangedTracker.h"
+#include "mozilla/ServoElementSnapshot.h"
+#include "mozilla/ServoElementSnapshotTable.h"
+#include "nsChangeHint.h"
+#include "nsPresContext.h"
+#include "nsPresContextInlines.h"  // XXX Shouldn't be included by header though
+#include "nsStringFwd.h"
+#include "nsTHashSet.h"
+
+class nsAttrValue;
+class nsAtom;
+class nsIFrame;
+class nsStyleChangeList;
+class nsStyleChangeList;
+
+namespace mozilla {
+
+class ServoStyleSet;
+
+namespace dom {
+class Element;
+}
+
+/**
+ * A stack class used to pass some common restyle state in a slightly more
+ * comfortable way than a bunch of individual arguments, and that also checks
+ * that the change hint used for optimization is correctly used in debug mode.
+ */
+class ServoRestyleState {
+ public:
+  ServoRestyleState(
+      ServoStyleSet& aStyleSet, nsStyleChangeList& aChangeList,
+      nsTArray<nsIFrame*>& aPendingWrapperRestyles,
+      nsTArray<RefPtr<dom::Element>>& aPendingScrollAnchorSuppressions)
+      : mStyleSet(aStyleSet),
+        mChangeList(aChangeList),
+        mPendingWrapperRestyles(aPendingWrapperRestyles),
+        mPendingScrollAnchorSuppressions(aPendingScrollAnchorSuppressions),
+        mPendingWrapperRestyleOffset(aPendingWrapperRestyles.Length()),
+        mChangesHandled(nsChangeHint(0))
+#ifdef DEBUG
+        // If !mOwner, then we wouldn't have processed our wrapper restyles,
+        // because we only process those when handling an element with a frame.
+        // But that's OK, because if we started our traversal at an element with
+        // no frame (e.g. it's display:contents), that means the wrapper frames
+        // in our list actually inherit from one of its ancestors, not from it,
+        // and hence not restyling them is OK.
+        ,
+        mAssertWrapperRestyleLength(false)
+#endif  // DEBUG
+  {
+  }
+
+  // We shouldn't assume that changes handled from our parent are handled for
+  // our children too if we're out of flow since they aren't necessarily
+  // parented in DOM order, and thus a change handled by a DOM ancestor doesn't
+  // necessarily mean that it's handled for an ancestor frame.
+  enum class Type {
+    InFlow,
+    OutOfFlow,
+  };
+
+  ServoRestyleState(const nsIFrame& aOwner, ServoRestyleState& aParentState,
+                    nsChangeHint aHintForThisFrame, Type aType,
+                    bool aAssertWrapperRestyleLength = true)
+      : mStyleSet(aParentState.mStyleSet),
+        mChangeList(aParentState.mChangeList),
+        mPendingWrapperRestyles(aParentState.mPendingWrapperRestyles),
+        mPendingScrollAnchorSuppressions(
+            aParentState.mPendingScrollAnchorSuppressions),
+        mPendingWrapperRestyleOffset(
+            aParentState.mPendingWrapperRestyles.Length()),
+        mChangesHandled(aType == Type::InFlow
+                            ? aParentState.mChangesHandled | aHintForThisFrame
+                            : aHintForThisFrame)
+#ifdef DEBUG
+        ,
+        mOwner(&aOwner),
+        mAssertWrapperRestyleLength(aAssertWrapperRestyleLength)
+#endif
+  {
+    if (aType == Type::InFlow) {
+      AssertOwner(aParentState);
+    }
+  }
+
+  ~ServoRestyleState() {
+    MOZ_ASSERT(
+        !mAssertWrapperRestyleLength ||
+            mPendingWrapperRestyles.Length() == mPendingWrapperRestyleOffset,
+        "Someone forgot to call ProcessWrapperRestyles!");
+  }
+
+  nsStyleChangeList& ChangeList() { return mChangeList; }
+  ServoStyleSet& StyleSet() { return mStyleSet; }
+
+#ifdef DEBUG
+  void AssertOwner(const ServoRestyleState& aParentState) const;
+  nsChangeHint ChangesHandledFor(const nsIFrame*) const;
+#else
+  void AssertOwner(const ServoRestyleState&) const {}
+  nsChangeHint ChangesHandledFor(const nsIFrame*) const {
+    return mChangesHandled;
+  }
+#endif
+
+  // Add a pending wrapper restyle.  We don't have to do anything if the thing
+  // being added is already last in the list, but otherwise we do want to add
+  // it, in order for ProcessWrapperRestyles to work correctly.
+  void AddPendingWrapperRestyle(nsIFrame* aWrapperFrame);
+
+  // Process wrapper restyles for this restyle state.  This should be done
+  // before it comes off the stack.
+  void ProcessWrapperRestyles(nsIFrame* aParentFrame);
+
+  // Get the table-aware parent for the given child.  This will walk through
+  // outer table and cellcontent frames.
+  static nsIFrame* TableAwareParentFor(const nsIFrame* aChild);
+
+  // When the value of the position property changes such as we stop or start
+  // being absolutely or fixed positioned, we need to suppress scroll anchoring
+  // adjustments to avoid breaking websites.
+  //
+  // We do need to process all this once we're done with all our reframes,
+  // to handle correctly the cases where we reconstruct an ancestor, like when
+  // you reframe an ib-split (see bug 1559627 for example).
+  //
+  // This doesn't handle nested reframes. We'd need to rework quite some code to
+  // do that, and so far it doesn't seem to be a problem in practice.
+  void AddPendingScrollAnchorSuppression(dom::Element* aElement) {
+    mPendingScrollAnchorSuppressions.AppendElement(aElement);
+  }
+
+ private:
+  // Process a wrapper restyle at the given index, and restyles for any
+  // wrappers nested in it.  Returns the number of entries from
+  // mPendingWrapperRestyles that we processed.  The return value is always at
+  // least 1.
+  size_t ProcessMaybeNestedWrapperRestyle(nsIFrame* aParent, size_t aIndex);
+
+  ServoStyleSet& mStyleSet;
+  nsStyleChangeList& mChangeList;
+
+  // A list of pending wrapper restyles.  Anonymous box wrapper frames that need
+  // restyling are added to this list when their non-anonymous kids are
+  // restyled.  This avoids us having to do linear searches along the frame tree
+  // for these anonymous boxes.  The problem then becomes that we can have
+  // multiple kids all with the same anonymous parent, and we don't want to
+  // restyle it more than once.  We use mPendingWrapperRestyles to track which
+  // anonymous wrapper boxes we've requested be restyled and which of them have
+  // already been restyled.  We use a single array propagated through
+  // ServoRestyleStates by reference, because in a situation like this:
+  //
+  //  <div style="display: table"><span></span></div>
+  //
+  // We have multiple wrappers to restyle (cell, row, table-row-group) and we
+  // want to add them in to the list all at once but restyle them using
+  // different ServoRestyleStates with different owners.  When this situation
+  // occurs, the relevant frames will be placed in the array with ancestors
+  // before descendants.
+  nsTArray<nsIFrame*>& mPendingWrapperRestyles;
+
+  nsTArray<RefPtr<dom::Element>>& mPendingScrollAnchorSuppressions;
+
+  // Since we're given a possibly-nonempty mPendingWrapperRestyles to start
+  // with, we need to keep track of where the part of it we're responsible for
+  // starts.
+  size_t mPendingWrapperRestyleOffset;
+
+  const nsChangeHint mChangesHandled;
+
+  // We track the "owner" frame of this restyle state, that is, the frame that
+  // generated the last change that is stored in mChangesHandled, in order to
+  // verify that we only use mChangesHandled for actual descendants of that
+  // frame (given DOM order isn't always frame order, and that there are a few
+  // special cases for stuff like wrapper frames, ::backdrop, and so on).
+#ifdef DEBUG
+  const nsIFrame* mOwner{nullptr};
+#endif
+
+  // Whether we should assert in our destructor that we've processed all of the
+  // relevant wrapper restyles.
+#ifdef DEBUG
+  const bool mAssertWrapperRestyleLength;
+#endif  // DEBUG
+};
+
+enum class ServoPostTraversalFlags : uint32_t;
+
+class RestyleManager {
+  friend class ServoStyleSet;
+
+ public:
+  typedef ServoElementSnapshotTable SnapshotTable;
+  typedef mozilla::dom::Element Element;
+
+  // Get an integer that increments every time we process pending restyles.
+  // The value is never 0.
+  uint64_t GetRestyleGeneration() const { return mRestyleGeneration; }
+  // Unlike GetRestyleGeneration, which means the actual restyling count,
+  // GetUndisplayedRestyleGeneration represents any possible DOM changes that
+  // can cause restyling. This is needed for getComputedStyle to work with
+  // non-styled (e.g. display: none) elements.
+  uint64_t GetUndisplayedRestyleGeneration() const {
+    return mUndisplayedRestyleGeneration;
+  }
+
+  void Disconnect() { mPresContext = nullptr; }
+
+  ~RestyleManager() {
+    MOZ_ASSERT(!mAnimationsWithDestroyedFrame,
+               "leaving dangling pointers from AnimationsWithDestroyedFrame");
+    MOZ_ASSERT(!mReentrantChanges);
+  }
+
+#ifdef DEBUG
+  static nsCString ChangeHintToString(nsChangeHint aHint);
+
+  /**
+   * DEBUG ONLY method to verify integrity of style tree versus frame tree
+   */
+  void DebugVerifyStyleTree(nsIFrame* aFrame);
+#endif
+
+  void FlushOverflowChangedTracker() { mOverflowChangedTracker.Flush(); }
+
+  // Should be called when a frame is going to be destroyed and
+  // WillDestroyFrameTree hasn't been called yet.
+  void NotifyDestroyingFrame(nsIFrame* aFrame) {
+    mOverflowChangedTracker.RemoveFrame(aFrame);
+    // If ProcessRestyledFrames is tracking frames which have been
+    // destroyed (to avoid re-visiting them), add this one to its set.
+    if (mDestroyedFrames) {
+      mDestroyedFrames->Insert(aFrame);
+    }
+  }
+
+  // Note: It's the caller's responsibility to make sure to wrap a
+  // ProcessRestyledFrames call in a view update batch and a script blocker.
+  // This function does not call ProcessAttachedQueue() on the binding manager.
+  // If the caller wants that to happen synchronously, it needs to handle that
+  // itself.
+  void ProcessRestyledFrames(nsStyleChangeList& aChangeList);
+
+  bool IsInStyleRefresh() const { return mInStyleRefresh; }
+
+  // AnimationsWithDestroyedFrame is used to stop animations and transitions
+  // on elements that have no frame at the end of the restyling process.
+  // It only lives during the restyling process.
+  class MOZ_STACK_CLASS AnimationsWithDestroyedFrame final {
+   public:
+    // Construct a AnimationsWithDestroyedFrame object.  The caller must
+    // ensure that aRestyleManager lives at least as long as the
+    // object.  (This is generally easy since the caller is typically a
+    // method of RestyleManager.)
+    explicit AnimationsWithDestroyedFrame(RestyleManager* aRestyleManager);
+
+    // This method takes the content node for the generated content for
+    // animation/transition on ::before and ::after, rather than the
+    // content node for the real element.
+    void Put(nsIContent* aContent, ComputedStyle* aComputedStyle) {
+      MOZ_ASSERT(aContent);
+      PseudoStyleType pseudoType = aComputedStyle->GetPseudoType();
+      if (pseudoType == PseudoStyleType::NotPseudo) {
+        mContents.AppendElement(aContent);
+      } else if (pseudoType == PseudoStyleType::before) {
+        MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
+                   nsGkAtoms::mozgeneratedcontentbefore);
+        mBeforeContents.AppendElement(aContent->GetParent());
+      } else if (pseudoType == PseudoStyleType::after) {
+        MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
+                   nsGkAtoms::mozgeneratedcontentafter);
+        mAfterContents.AppendElement(aContent->GetParent());
+      } else if (pseudoType == PseudoStyleType::marker) {
+        MOZ_ASSERT(aContent->NodeInfo()->NameAtom() ==
+                   nsGkAtoms::mozgeneratedcontentmarker);
+        mMarkerContents.AppendElement(aContent->GetParent());
+      }
+    }
+
+    void StopAnimationsForElementsWithoutFrames();
+
+   private:
+    void StopAnimationsWithoutFrame(nsTArray<RefPtr<nsIContent>>& aArray,
+                                    PseudoStyleType aPseudoType);
+
+    RestyleManager* mRestyleManager;
+    AutoRestore<AnimationsWithDestroyedFrame*> mRestorePointer;
+
+    // Below three arrays might include elements that have already had their
+    // animations or transitions stopped.
+    //
+    // mBeforeContents, mAfterContents and mMarkerContents hold the real element
+    // rather than the content node for the generated content (which might
+    // change during a reframe)
+    nsTArray<RefPtr<nsIContent>> mContents;
+    nsTArray<RefPtr<nsIContent>> mBeforeContents;
+    nsTArray<RefPtr<nsIContent>> mAfterContents;
+    nsTArray<RefPtr<nsIContent>> mMarkerContents;
+  };
+
+  /**
+   * Return the current AnimationsWithDestroyedFrame struct, or null if we're
+   * not currently in a restyling operation.
+   */
+  AnimationsWithDestroyedFrame* GetAnimationsWithDestroyedFrame() {
+    return mAnimationsWithDestroyedFrame;
+  }
+
+  void ContentInserted(nsIContent* aChild);
+  void ContentAppended(nsIContent* aFirstNewContent);
+
+  // This would be have the same logic as RestyleForInsertOrChange if we got the
+  // notification before the removal.  However, we get it after, so we need the
+  // following sibling in addition to the old child.
+  //
+  // aFollowingSibling is the sibling that used to come after aOldChild before
+  // the removal.
+  void ContentRemoved(nsIContent* aOldChild, nsIContent* aFollowingSibling);
+
+  // Restyling for a ContentInserted (notification after insertion) or
+  // for some CharacterDataChanged.
+  void RestyleForInsertOrChange(nsIContent* aChild);
+
+  // Restyle for a CharacterDataChanged notification. In practice this can only
+  // affect :empty / :-moz-only-whitespace / :-moz-first-node / :-moz-last-node.
+  void CharacterDataChanged(nsIContent*, const CharacterDataChangeInfo&);
+
+  void PostRestyleEvent(dom::Element*, RestyleHint,
+                        nsChangeHint aMinChangeHint);
+
+  /**
+   * Posts restyle hints for animations.
+   * This is only called for the second traversal for CSS animations during
+   * updating CSS animations in a SequentialTask.
+   * This function does neither register a refresh observer nor flag that a
+   * style flush is needed since this function is supposed to be called during
+   * restyling process and this restyle event will be processed in the second
+   * traversal of the same restyling process.
+   */
+  void PostRestyleEventForAnimations(dom::Element*, PseudoStyleType,
+                                     RestyleHint);
+
+  void NextRestyleIsForCSSRuleChanges() { mRestyleForCSSRuleChanges = true; }
+
+  void RebuildAllStyleData(nsChangeHint aExtraHint, RestyleHint);
+
+  void ProcessPendingRestyles();
+  void ProcessAllPendingAttributeAndStateInvalidations();
+
+  void ElementStateChanged(Element*, dom::ElementState);
+
+  /**
+   * Posts restyle hints for siblings of an element and their descendants if the
+   * element's parent has NODE_HAS_SLOW_SELECTOR_NTH_OF and the element has a
+   * relevant state dependency.
+   */
+  void MaybeRestyleForNthOfState(ServoStyleSet& aStyleSet, dom::Element* aChild,
+                                 dom::ElementState aChangedBits);
+
+  void AttributeWillChange(Element* aElement, int32_t aNameSpaceID,
+                           nsAtom* aAttribute, int32_t aModType);
+  void ClassAttributeWillBeChangedBySMIL(dom::Element* aElement);
+  void AttributeChanged(dom::Element* aElement, int32_t aNameSpaceID,
+                        nsAtom* aAttribute, int32_t aModType,
+                        const nsAttrValue* aOldValue);
+
+  /**
+   * Restyle an element's previous and/or next siblings.
+   */
+  void RestyleSiblingsForNthOf(dom::Element* aChild,
+                               NodeSelectorFlags aParentFlags);
+
+  /**
+   * Posts restyle hints for siblings of an element and their descendants if the
+   * element's parent has NODE_HAS_SLOW_SELECTOR_NTH_OF and the element has a
+   * relevant attribute dependency.
+   */
+  void MaybeRestyleForNthOfAttribute(dom::Element* aChild, nsAtom* aAttribute,
+                                     const nsAttrValue* aOldValue);
+
+  void MaybeRestyleForRelativeSelectorAttribute(dom::Element* aElement,
+                                                nsAtom* aAttribute,
+                                                const nsAttrValue* aOldValue);
+  void MaybeRestyleForRelativeSelectorState(ServoStyleSet& aStyleSet,
+                                            dom::Element* aElement,
+                                            dom::ElementState aChangedBits);
+
+  // This is only used to reparent things when moving them in/out of the
+  // ::first-line.
+  void ReparentComputedStyleForFirstLine(nsIFrame*);
+
+  /**
+   * Performs a Servo animation-only traversal to compute style for all nodes
+   * with the animation-only dirty bit in the document.
+   *
+   * This processes just the traversal for animation-only restyles and skips the
+   * normal traversal for other restyles unrelated to animations.
+   * This is used to bring throttled animations up-to-date such as when we need
+   * to get correct position for transform animations that are throttled because
+   * they are running on the compositor.
+   *
+   * This will traverse all of the document's style roots (that is, its document
+   * element, and the roots of the document-level native anonymous content).
+   */
+  void UpdateOnlyAnimationStyles();
+
+  // Get a counter that increments on every style change, that we use to
+  // track whether off-main-thread animations are up-to-date.
+  uint64_t GetAnimationGeneration() const { return mAnimationGeneration; }
+
+  // Typically only style frames have animations associated with them so this
+  // will likely return zero for anything that is not a style frame.
+  static uint64_t GetAnimationGenerationForFrame(nsIFrame* aStyleFrame);
+
+  // Update the animation generation count to mark that animation state
+  // has changed.
+  //
+  // This is normally performed automatically by ProcessPendingRestyles
+  // but it is also called when we have out-of-band changes to animations
+  // such as changes made through the Web Animations API.
+  void IncrementAnimationGeneration();
+
+  // Apply change hints for animations on the compositor.
+  //
+  // There are some cases where we forcibly apply change hints for animations
+  // even if there is no change hint produced in order to synchronize with
+  // animations running on the compositor.
+  //
+  // For example:
+  //
+  // a) Pausing animations via the Web Animations API
+  // b) When the style before sending the animation to the compositor exactly
+  // the same as the current style
+  static void AddLayerChangesForAnimation(
+      nsIFrame* aStyleFrame, nsIFrame* aPrimaryFrame, Element* aElement,
+      nsChangeHint aHintForThisFrame, nsStyleChangeList& aChangeListToProcess);
+
+  /**
+   * Whether to clear all the style data (including the element itself), or just
+   * the descendants' data.
+   */
+  enum class IncludeRoot {
+    Yes,
+    No,
+  };
+
+  /**
+   * Clears the ServoElementData and HasDirtyDescendants from all elements
+   * in the subtree rooted at aElement.
+   */
+  static void ClearServoDataFromSubtree(Element*,
+                                        IncludeRoot = IncludeRoot::Yes);
+
+  /**
+   * Clears HasDirtyDescendants and RestyleData from all elements in the
+   * subtree rooted at aElement.
+   */
+  static void ClearRestyleStateFromSubtree(Element* aElement);
+
+  explicit RestyleManager(nsPresContext* aPresContext);
+
+ protected:
+  /**
+   * Reparent the descendants of aFrame.  This is used by ReparentComputedStyle
+   * and shouldn't be called by anyone else.  aProviderChild, if non-null, is a
+   * child that was the style parent for aFrame and hence shouldn't be
+   * reparented.
+   */
+  void ReparentFrameDescendants(nsIFrame* aFrame, nsIFrame* aProviderChild,
+                                ServoStyleSet& aStyleSet);
+
+  /**
+   * Performs post-Servo-traversal processing on this element and its
+   * descendants.
+   *
+   * Returns whether any style did actually change. There may be cases where we
+   * didn't need to change any style after all, for example, when a content
+   * attribute changes that happens not to have any effect on the style of that
+   * element or any descendant or sibling.
+   */
+  bool ProcessPostTraversal(Element* aElement, ServoRestyleState& aRestyleState,
+                            ServoPostTraversalFlags aFlags);
+
+  struct TextPostTraversalState;
+  bool ProcessPostTraversalForText(nsIContent* aTextNode,
+                                   TextPostTraversalState& aState,
+                                   ServoRestyleState& aRestyleState,
+                                   ServoPostTraversalFlags aFlags);
+
+  ServoStyleSet* StyleSet() const { return PresContext()->StyleSet(); }
+
+  void RestylePreviousSiblings(nsIContent* aStartingSibling);
+  void RestyleSiblingsStartingWith(nsIContent* aStartingSibling);
+
+  void RestyleForEmptyChange(Element* aContainer);
+  void MaybeRestyleForEdgeChildChange(nsINode* aContainer,
+                                      nsIContent* aChangedChild);
+
+  bool IsDisconnected() const { return !mPresContext; }
+
+  void IncrementRestyleGeneration() {
+    if (++mRestyleGeneration == 0) {
+      // Keep mRestyleGeneration from being 0, since that's what
+      // nsPresContext::GetRestyleGeneration returns when it no
+      // longer has a RestyleManager.
+      ++mRestyleGeneration;
+    }
+    IncrementUndisplayedRestyleGeneration();
+  }
+
+  void IncrementUndisplayedRestyleGeneration() {
+    if (++mUndisplayedRestyleGeneration == 0) {
+      // Ensure mUndisplayedRestyleGeneration > 0, for the same reason as
+      // IncrementRestyleGeneration.
+      ++mUndisplayedRestyleGeneration;
+    }
+  }
+
+  nsPresContext* PresContext() const {
+    MOZ_ASSERT(mPresContext);
+    return mPresContext;
+  }
+
+ private:
+  nsPresContext* mPresContext;  // weak, can be null after Disconnect().
+  uint64_t mRestyleGeneration;
+  uint64_t mUndisplayedRestyleGeneration;
+
+  // Used to keep track of frames that have been destroyed during
+  // ProcessRestyledFrames, so we don't try to touch them again even if
+  // they're referenced again later in the changelist.
+  mozilla::UniquePtr<nsTHashSet<const nsIFrame*>> mDestroyedFrames;
+
+ protected:
+  // True if we're in the middle of a nsRefreshDriver refresh
+  bool mInStyleRefresh;
+
+  // The total number of animation flushes by this frame constructor.
+  // Used to keep the layer and animation manager in sync.
+  uint64_t mAnimationGeneration;
+
+  OverflowChangedTracker mOverflowChangedTracker;
+
+  AnimationsWithDestroyedFrame* mAnimationsWithDestroyedFrame = nullptr;
+
+  const SnapshotTable& Snapshots() const { return mSnapshots; }
+  void ClearSnapshots();
+  ServoElementSnapshot& SnapshotFor(Element&);
+  void TakeSnapshotForAttributeChange(Element&, int32_t aNameSpaceID,
+                                      nsAtom* aAttribute);
+
+  void DoProcessPendingRestyles(ServoTraversalFlags aFlags);
+
+  // Function to do the actual (recursive) work of
+  // ReparentComputedStyleForFirstLine, once we have asserted the invariants
+  // that only hold on the initial call.
+  void DoReparentComputedStyleForFirstLine(nsIFrame*, ServoStyleSet&);
+
+  // We use a separate data structure from nsStyleChangeList because we need a
+  // frame to create nsStyleChangeList entries, and the primary frame may not be
+  // attached yet.
+  struct ReentrantChange {
+    nsCOMPtr<nsIContent> mContent;
+    nsChangeHint mHint;
+  };
+  typedef AutoTArray<ReentrantChange, 10> ReentrantChangeList;
+
+  // Only non-null while processing change hints. See the comment in
+  // ProcessPendingRestyles.
+  ReentrantChangeList* mReentrantChanges = nullptr;
+
+  // We use this flag to track if the current restyle contains any non-animation
+  // update, which triggers a normal restyle, and so there might be any new
+  // transition created later. Therefore, if this flag is true, we need to
+  // increase mAnimationGeneration before creating new transitions, so their
+  // creation sequence will be correct.
+  bool mHaveNonAnimationRestyles = false;
+
+  // Set to true when posting restyle events triggered by CSS rule changes.
+  // This flag is cleared once ProcessPendingRestyles has completed.
+  // When we process a traversal all descendants elements of the document
+  // triggered by CSS rule changes, we will need to update all elements with
+  // CSS animations.  We propagate TraversalRestyleBehavior::ForCSSRuleChanges
+  // to traversal function if this flag is set.
+  bool mRestyleForCSSRuleChanges = false;
+
+  // A hashtable with the elements that have changed state or attributes, in
+  // order to calculate restyle hints during the traversal.
+  SnapshotTable mSnapshots;
+};
+
+}  // namespace mozilla
+
+#endif