compositor: Tick the UI animations from cc, instead of from timer callbacks.

ui/compositor/layer.h

Index: ui/compositor/layer.h
diff --git a/ui/compositor/layer.h b/ui/compositor/layer.h
index 2b0d9138361dd46eabb0dbe199716c63c2256f3e..e2757f973f98ed2ed0b0068c9e47800e21f75f65 100644
--- a/ui/compositor/layer.h
+++ b/ui/compositor/layer.h
@@ -366,6 +366,7 @@ class COMPOSITOR_EXPORT Layer
   virtual void AddThreadedAnimation(
       scoped_ptr<cc::Animation> animation) OVERRIDE;
   virtual void RemoveThreadedAnimation(int animation_id) OVERRIDE;
+  virtual LayerAnimatorCollection* GetLayerAnimatorCollection() OVERRIDE;
 
   // Creates a corresponding composited layer for |type_|.
   void CreateWebLayer();
@@ -389,6 +390,9 @@ class COMPOSITOR_EXPORT Layer
   // be called once we have been added to a tree.
   void SendPendingThreadedAnimations();
 
+  // Returns whether the layer has an animating LayerAnimator.
+  bool IsAnimating() const;
+
   const LayerType type_;
 
   Compositor* compositor_;