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diff --git a/dom/smil/SMILAnimationController.h b/dom/smil/SMILAnimationController.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 DOM_SMIL_SMILANIMATIONCONTROLLER_H_
+#define DOM_SMIL_SMILANIMATIONCONTROLLER_H_
+
+#include "mozilla/Attributes.h"
+#include "mozilla/SMILCompositorTable.h"
+#include "mozilla/SMILMilestone.h"
+#include "mozilla/SMILTimeContainer.h"
+#include "mozilla/UniquePtr.h"
+#include "nsCOMPtr.h"
+#include "nsTArray.h"
+#include "nsTHashtable.h"
+#include "nsHashKeys.h"
+#include "nsRefreshObservers.h"
+
+class nsRefreshDriver;
+
+namespace mozilla {
+struct SMILTargetIdentifier;
+namespace dom {
+class Element;
+class SVGAnimationElement;
+}  // namespace dom
+
+//----------------------------------------------------------------------
+// SMILAnimationController
+//
+// The animation controller maintains the animation timer and determines the
+// sample times and sample rate for all SMIL animations in a document. There is
+// at most one animation controller per document so that frame-rate tuning can
+// be performed at a document-level.
+//
+// The animation controller can contain many child time containers (timed
+// document root objects) which may correspond to SVG document fragments within
+// a compound document. These time containers can be paused individually or
+// here, at the document level.
+//
+class SMILAnimationController final : public SMILTimeContainer,
+                                      public nsARefreshObserver {
+ public:
+  explicit SMILAnimationController(mozilla::dom::Document* aDoc);
+
+  // Clears mDocument pointer. (Called by our mozilla::dom::Document when it's
+  // going away)
+  void Disconnect();
+
+  // SMILContainer
+  void Pause(uint32_t aType) override;
+  void Resume(uint32_t aType) override;
+  SMILTime GetParentTime() const override;
+
+  // nsARefreshObserver
+  NS_IMETHOD_(MozExternalRefCountType) AddRef() override;
+  NS_IMETHOD_(MozExternalRefCountType) Release() override;
+
+  void WillRefresh(mozilla::TimeStamp aTime) override;
+
+  // Methods for registering and enumerating animation elements
+  void RegisterAnimationElement(
+      mozilla::dom::SVGAnimationElement* aAnimationElement);
+  void UnregisterAnimationElement(
+      mozilla::dom::SVGAnimationElement* aAnimationElement);
+
+  // Methods for resampling all animations
+  // (A resample performs the same operations as a sample but doesn't advance
+  // the current time and doesn't check if the container is paused)
+  // This will flush pending style changes for the document.
+  void Resample() { DoSample(false); }
+
+  void SetResampleNeeded() {
+    if (!mRunningSample && !mResampleNeeded) {
+      FlagDocumentNeedsFlush();
+      mResampleNeeded = true;
+    }
+  }
+
+  // This will flush pending style changes for the document.
+  void FlushResampleRequests() {
+    if (!mResampleNeeded) return;
+
+    Resample();
+  }
+
+  // Methods for handling page transitions
+  void OnPageShow();
+  void OnPageHide();
+
+  // Methods for supporting cycle-collection
+  void Traverse(nsCycleCollectionTraversalCallback* aCallback);
+  void Unlink();
+
+  // Methods for relaying the availability of the refresh driver
+  void NotifyRefreshDriverCreated(nsRefreshDriver* aRefreshDriver);
+  void NotifyRefreshDriverDestroying(nsRefreshDriver* aRefreshDriver);
+
+  // Helper to check if we have any animation elements at all
+  bool HasRegisteredAnimations() const {
+    return mAnimationElementTable.Count() != 0;
+  }
+
+  bool MightHavePendingStyleUpdates() const {
+    return mMightHavePendingStyleUpdates;
+  }
+
+  bool PreTraverse();
+  bool PreTraverseInSubtree(mozilla::dom::Element* aRoot);
+
+ protected:
+  ~SMILAnimationController();
+
+  // alias declarations
+  using TimeContainerPtrKey = nsPtrHashKey<SMILTimeContainer>;
+  using TimeContainerHashtable = nsTHashtable<TimeContainerPtrKey>;
+  using AnimationElementPtrKey = nsPtrHashKey<dom::SVGAnimationElement>;
+  using AnimationElementHashtable = nsTHashtable<AnimationElementPtrKey>;
+
+  // Returns mDocument's refresh driver, if it's got one.
+  nsRefreshDriver* GetRefreshDriver();
+
+  // Methods for controlling whether we're sampling
+  void StartSampling(nsRefreshDriver* aRefreshDriver);
+  void StopSampling(nsRefreshDriver* aRefreshDriver);
+
+  // Wrapper for StartSampling that defers if no animations are registered.
+  void MaybeStartSampling(nsRefreshDriver* aRefreshDriver);
+
+  // Sample-related callbacks and implementation helpers
+  void DoSample() override;
+  void DoSample(bool aSkipUnchangedContainers);
+
+  void RewindElements();
+
+  void DoMilestoneSamples();
+
+  static void SampleTimedElement(mozilla::dom::SVGAnimationElement* aElement,
+                                 TimeContainerHashtable* aActiveContainers);
+
+  static void AddAnimationToCompositorTable(
+      mozilla::dom::SVGAnimationElement* aElement,
+      SMILCompositorTable* aCompositorTable, bool& aStyleFlushNeeded);
+
+  static bool GetTargetIdentifierForAnimation(
+      mozilla::dom::SVGAnimationElement* aAnimElem,
+      SMILTargetIdentifier& aResult);
+
+  // Methods for adding/removing time containers
+  nsresult AddChild(SMILTimeContainer& aChild) override;
+  void RemoveChild(SMILTimeContainer& aChild) override;
+
+  void FlagDocumentNeedsFlush();
+
+  // Members
+  nsAutoRefCnt mRefCnt;
+  NS_DECL_OWNINGTHREAD
+
+  AnimationElementHashtable mAnimationElementTable;
+  TimeContainerHashtable mChildContainerTable;
+  mozilla::TimeStamp mCurrentSampleTime;
+  mozilla::TimeStamp mStartTime;
+
+  // Average time between samples from the refresh driver. This is used to
+  // detect large unexpected gaps between samples such as can occur when the
+  // computer sleeps. The nature of the SMIL model means that catching up these
+  // large gaps can be expensive as, for example, many events may need to be
+  // dispatched for the intervening time when no samples were received.
+  //
+  // In such cases, we ignore the intervening gap and continue sampling from
+  // when we were expecting the next sample to arrive.
+  //
+  // Note that we only do this for SMIL and not CSS transitions (which doesn't
+  // have so much work to do to catch up) nor scripted animations (which expect
+  // animation time to follow real time).
+  //
+  // This behaviour does not affect pausing (since we're not *expecting* any
+  // samples then) nor seeking (where the SMIL model behaves somewhat
+  // differently such as not dispatching events).
+  SMILTime mAvgTimeBetweenSamples;
+
+  bool mResampleNeeded;
+  // If we're told to start sampling but there are no animation elements we just
+  // record the time, set the following flag, and then wait until we have an
+  // animation element. Then we'll reset this flag and actually start sampling.
+  bool mDeferredStartSampling;
+  bool mRunningSample;
+
+  // Are we registered with our document's refresh driver?
+  bool mRegisteredWithRefreshDriver;
+
+  // Have we updated animated values without adding them to the restyle tracker?
+  bool mMightHavePendingStyleUpdates;
+
+  // Store raw ptr to mDocument.  It owns the controller, so controller
+  // shouldn't outlive it
+  mozilla::dom::Document* mDocument;
+
+  // Contains compositors used in our last sample.  We keep this around
+  // so we can detect when an element/attribute used to be animated,
+  // but isn't anymore for some reason. (e.g. if its <animate> element is
+  // removed or retargeted)
+  UniquePtr<SMILCompositorTable> mLastCompositorTable;
+};
+
+}  // namespace mozilla
+
+#endif  // DOM_SMIL_SMILANIMATIONCONTROLLER_H_