Share animations from compositor to main thread.

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

 /*
  * Copyright (c) 2011, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 49 matching lines @@
     void cancelAnimation() override;
     void resetAnimationState() override;
     void updateCompositorAnimations() override;
     void notifyCompositorAnimationFinished(int groupId) override;
     void notifyCompositorAnimationAborted(int groupId) override;
     void layerForCompositedScrollingDidChange(CompositorAnimationTimeline*) override;
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
+    void notifyAnimationTakeover(
+        double monotonicTime,
+        double animationStartTime,
+        scoped_ptr<cc::AnimationCurve>) override;
+
     OwnPtr<CompositorScrollOffsetAnimationCurve> m_animationCurve;
     double m_startTime;
     WTF::TimeFunction m_timeFunction;
 
 private:
     // Returns true if the animation was scheduled successfully. If animation
     // could not be scheduled (e.g. because the frame is detached), scrolls
     // immediately to the target and returns false.
     bool registerAndScheduleAnimation();
 
     void postAnimationCleanupAndReset();
 
     void addMainThreadScrollingReason();
     void removeMainThreadScrollingReason();
 
+    // Returns true if will animate to the given target position.

[ajuma, 2016/02/26 23:56:54]

Please expand this to include the sorts of things that would cause us to animate
or not animate.

[ymalik, 2016/02/29 16:31:09]

Done.

+    bool willAnimateToOffset(const FloatPoint& targetPos);
+
     FloatPoint m_targetOffset;
     ScrollGranularity m_lastGranularity;
 };
 
 } // namespace blink
 
 #endif // ScrollAnimator_h