Fix smooth scroll jump when switching scroll handling between MT and CC

third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ScrollAnimatorCompositorCoordinator_h
 #define ScrollAnimatorCompositorCoordinator_h
 
 #include "base/gtest_prod_util.h"
 #include "platform/PlatformExport.h"
 #include "platform/heap/Handle.h"
@@ skipping 10 matching lines @@
 class WebCompositorAnimationTimeline;
 
 class PLATFORM_EXPORT ScrollAnimatorCompositorCoordinator : public NoBaseWillBeGarbageCollectedFinalized<ScrollAnimatorCompositorCoordinator>, private WebCompositorAnimationPlayerClient, WebCompositorAnimationDelegate {
     USING_FAST_MALLOC_WILL_BE_REMOVED(ScrollAnimatorCompositorCoordinator);
     WTF_MAKE_NONCOPYABLE(ScrollAnimatorCompositorCoordinator);
 public:
     virtual ~ScrollAnimatorCompositorCoordinator();
 
     bool hasAnimationThatRequiresService() const;
 
+    virtual bool hasRunningAnimation() const { return false; }
+
     virtual void resetAnimationState();
     virtual void cancelAnimation();
 
     virtual ScrollableArea* scrollableArea() const = 0;
     virtual void tickAnimation(double monotonicTime) = 0;
     virtual void updateCompositorAnimations() = 0;
     virtual void notifyCompositorAnimationFinished(int groupId) = 0;
     virtual void notifyCompositorAnimationAborted(int groupId) = 0;
     virtual void layerForCompositedScrollingDidChange(WebCompositorAnimationTimeline*) = 0;
 
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
 protected:
     explicit ScrollAnimatorCompositorCoordinator();
 
     bool addAnimation(PassOwnPtr<WebCompositorAnimation>);
     void removeAnimation();
     void abortAnimation();
 
     void compositorAnimationFinished(int groupId);
-    void reattachCompositorPlayerIfNeeded(WebCompositorAnimationTimeline*);
+    // Returns true if the compositor player was attached to a new layer.
+    bool reattachCompositorPlayerIfNeeded(WebCompositorAnimationTimeline*);
 
     // WebCompositorAnimationDelegate implementation.
     void notifyAnimationStarted(double monotonicTime, int group) override;
     void notifyAnimationFinished(double monotonicTime, int group) override;
     void notifyAnimationAborted(double monotonicTime, int group) override;
 
     // WebCompositorAnimationPlayerClient implementation.
     WebCompositorAnimationPlayer* compositorPlayer() const override;
 
     friend class Internals;
@@ skipping 30 matching lines @@
     OwnPtr<WebCompositorAnimationPlayer> m_compositorPlayer;
     int m_compositorAnimationAttachedToLayerId;
     RunState m_runState;
     int m_compositorAnimationId;
     int m_compositorAnimationGroupId;
 };
 
 } // namespace blink
 
 #endif // ScrollAnimatorCompositorCoordinator_h