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diff --git a/layout/style/AnimationCommon.h b/layout/style/AnimationCommon.h
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+++ b/layout/style/AnimationCommon.h
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+/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
+/* 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_css_AnimationCommon_h
+#define mozilla_css_AnimationCommon_h
+
+#include <algorithm> // For <std::stable_sort>
+#include "mozilla/AnimationCollection.h"
+#include "mozilla/AnimationComparator.h"
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/LinkedList.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/dom/Animation.h"
+#include "mozilla/Attributes.h" // For MOZ_NON_OWNING_REF
+#include "mozilla/Assertions.h"
+#include "nsContentUtils.h"
+#include "nsCSSPseudoElements.h"
+#include "nsCycleCollectionParticipant.h"
+
+class nsIFrame;
+class nsPresContext;
+
+namespace mozilla {
+
+namespace dom {
+class Element;
+}
+
+template <class AnimationType>
+class CommonAnimationManager {
+public:
+  explicit CommonAnimationManager(nsPresContext *aPresContext)
+    : mPresContext(aPresContext)
+  {
+  }
+
+  // NOTE:  This can return null after Disconnect().
+  nsPresContext* PresContext() const { return mPresContext; }
+
+  /**
+   * Notify the manager that the pres context is going away.
+   */
+  void Disconnect()
+  {
+    // Content nodes might outlive the transition or animation manager.
+    RemoveAllElementCollections();
+
+    mPresContext = nullptr;
+  }
+
+protected:
+  virtual ~CommonAnimationManager()
+  {
+    MOZ_ASSERT(!mPresContext, "Disconnect should have been called");
+  }
+
+  void AddElementCollection(AnimationCollection<AnimationType>* aCollection)
+  {
+    mElementCollections.insertBack(aCollection);
+  }
+  void RemoveAllElementCollections()
+  {
+    while (AnimationCollection<AnimationType>* head =
+           mElementCollections.getFirst()) {
+      head->Destroy(); // Note: this removes 'head' from mElementCollections.
+    }
+  }
+
+  LinkedList<AnimationCollection<AnimationType>> mElementCollections;
+  nsPresContext *mPresContext; // weak (non-null from ctor to Disconnect)
+};
+
+/**
+ * Utility class for referencing the element that created a CSS animation or
+ * transition. It is non-owning (i.e. it uses a raw pointer) since it is only
+ * expected to be set by the owned animation while it actually being managed
+ * by the owning element.
+ *
+ * This class also abstracts the comparison of an element/pseudo-class pair
+ * for the sake of composite ordering since this logic is common to both CSS
+ * animations and transitions.
+ *
+ * (We call this OwningElementRef instead of just OwningElement so that we can
+ * call the getter on CSSAnimation/CSSTransition OwningElement() without
+ * clashing with this object's contructor.)
+ */
+class OwningElementRef final
+{
+public:
+  OwningElementRef()
+    : mElement(nullptr)
+    , mPseudoType(CSSPseudoElementType::NotPseudo)
+  { }
+
+  OwningElementRef(dom::Element& aElement,
+                   CSSPseudoElementType aPseudoType)
+    : mElement(&aElement)
+    , mPseudoType(aPseudoType)
+  { }
+
+  bool Equals(const OwningElementRef& aOther) const
+  {
+    return mElement == aOther.mElement &&
+           mPseudoType == aOther.mPseudoType;
+  }
+
+  bool LessThan(const OwningElementRef& aOther) const
+  {
+    MOZ_ASSERT(mElement && aOther.mElement,
+               "Elements to compare should not be null");
+
+    if (mElement != aOther.mElement) {
+      return nsContentUtils::PositionIsBefore(mElement, aOther.mElement);
+    }
+
+    return mPseudoType == CSSPseudoElementType::NotPseudo ||
+          (mPseudoType == CSSPseudoElementType::before &&
+           aOther.mPseudoType == CSSPseudoElementType::after);
+  }
+
+  bool IsSet() const { return !!mElement; }
+
+  void GetElement(dom::Element*& aElement,
+                  CSSPseudoElementType& aPseudoType) const {
+    aElement = mElement;
+    aPseudoType = mPseudoType;
+  }
+
+  nsPresContext* GetRenderedPresContext() const;
+
+private:
+  dom::Element* MOZ_NON_OWNING_REF mElement;
+  CSSPseudoElementType             mPseudoType;
+};
+
+template <class EventInfo>
+class DelayedEventDispatcher
+{
+public:
+  DelayedEventDispatcher() : mIsSorted(true) { }
+
+  void QueueEvent(EventInfo&& aEventInfo)
+  {
+    mPendingEvents.AppendElement(Forward<EventInfo>(aEventInfo));
+    mIsSorted = false;
+  }
+
+  // This is exposed as a separate method so that when we are dispatching
+  // *both* transition events and animation events we can sort both lists
+  // once using the current state of the document before beginning any
+  // dispatch.
+  void SortEvents()
+  {
+    if (mIsSorted) {
+      return;
+    }
+
+    // FIXME: Replace with mPendingEvents.StableSort when bug 1147091 is
+    // fixed.
+    std::stable_sort(mPendingEvents.begin(), mPendingEvents.end(),
+                     EventInfoLessThan());
+    mIsSorted = true;
+  }
+
+  // Takes a reference to the owning manager's pres context so it can
+  // detect if the pres context is destroyed while dispatching one of
+  // the events.
+  //
+  // This will call SortEvents automatically if it has not already been
+  // called.
+  void DispatchEvents(nsPresContext* const & aPresContext)
+  {
+    if (!aPresContext || mPendingEvents.IsEmpty()) {
+      return;
+    }
+
+    SortEvents();
+
+    EventArray events;
+    mPendingEvents.SwapElements(events);
+    // mIsSorted will be set to true by SortEvents above, and we leave it
+    // that way since mPendingEvents is now empty
+    for (EventInfo& info : events) {
+      EventDispatcher::Dispatch(info.mElement, aPresContext, &info.mEvent);
+
+      if (!aPresContext) {
+        break;
+      }
+    }
+  }
+
+  void ClearEventQueue()
+  {
+    mPendingEvents.Clear();
+    mIsSorted = true;
+  }
+  bool HasQueuedEvents() const { return !mPendingEvents.IsEmpty(); }
+
+  // Methods for supporting cycle-collection
+  void Traverse(nsCycleCollectionTraversalCallback* aCallback,
+                const char* aName)
+  {
+    for (EventInfo& info : mPendingEvents) {
+      ImplCycleCollectionTraverse(*aCallback, info.mElement, aName);
+      ImplCycleCollectionTraverse(*aCallback, info.mAnimation, aName);
+    }
+  }
+  void Unlink() { ClearEventQueue(); }
+
+protected:
+  class EventInfoLessThan
+  {
+  public:
+    bool operator()(const EventInfo& a, const EventInfo& b) const
+    {
+      if (a.mTimeStamp != b.mTimeStamp) {
+        // Null timestamps sort first
+        if (a.mTimeStamp.IsNull() || b.mTimeStamp.IsNull()) {
+          return a.mTimeStamp.IsNull();
+        } else {
+          return a.mTimeStamp < b.mTimeStamp;
+        }
+      }
+
+      AnimationPtrComparator<RefPtr<dom::Animation>> comparator;
+      return comparator.LessThan(a.mAnimation, b.mAnimation);
+    }
+  };
+
+  typedef nsTArray<EventInfo> EventArray;
+  EventArray mPendingEvents;
+  bool mIsSorted;
+};
+
+template <class EventInfo>
+inline void
+ImplCycleCollectionUnlink(DelayedEventDispatcher<EventInfo>& aField)
+{
+  aField.Unlink();
+}
+
+template <class EventInfo>
+inline void
+ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
+                            DelayedEventDispatcher<EventInfo>& aField,
+                            const char* aName,
+                            uint32_t aFlags = 0)
+{
+  aField.Traverse(&aCallback, aName);
+}
+
+} // namespace mozilla
+
+#endif /* !defined(mozilla_css_AnimationCommon_h) */