compositor: Add rAF-like functionality for the UI.

ui/compositor/layer_animator_collection.h

Index: ui/compositor/layer_animator_collection.h
diff --git a/ui/compositor/layer_animator_collection.h b/ui/compositor/layer_animator_collection.h
index 2789eda3cb4fbdb9e7427714a307ce786253cc56..ecfda71819097b26ca4623dbd1d5fc350351b094 100644
--- a/ui/compositor/layer_animator_collection.h
+++ b/ui/compositor/layer_animator_collection.h
@@ -10,6 +10,7 @@
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
+#include "ui/compositor/animation_frame_task.h"
 #include "ui/compositor/compositor_export.h"
 
 namespace base {
@@ -20,33 +21,28 @@ namespace ui {
 
 class LayerAnimator;
 
-class COMPOSITOR_EXPORT LayerAnimatorCollectionDelegate {
- public:
-  virtual ~LayerAnimatorCollectionDelegate() {}
-
-  virtual void ScheduleAnimationForLayerCollection() = 0;
-};
-
 // A collection of LayerAnimators that should be updated at each animation step
 // in the compositor.
-class COMPOSITOR_EXPORT LayerAnimatorCollection {
+class COMPOSITOR_EXPORT LayerAnimatorCollection : public AnimationFrameTask {
  public:
-  explicit LayerAnimatorCollection(LayerAnimatorCollectionDelegate* delegate);
-  ~LayerAnimatorCollection();
+  explicit LayerAnimatorCollection(AnimationFrameTaskProvider* provider);
+  virtual ~LayerAnimatorCollection();
 
   void StartAnimator(scoped_refptr<LayerAnimator> animator);
   void StopAnimator(scoped_refptr<LayerAnimator> animator);
 
   bool HasActiveAnimators() const;
 
-  void Progress(base::TimeTicks now);
+  // AnimationFrameTask:
+  virtual AnimationFrameTaskStatus Progress(base::TimeTicks now) OVERRIDE;
 
   base::TimeTicks last_tick_time() const { return last_tick_time_; }
 
  private:
-  LayerAnimatorCollectionDelegate* delegate_;
+  AnimationFrameTaskProvider* provider_;
   base::TimeTicks last_tick_time_;
   std::set<scoped_refptr<LayerAnimator> > animators_;
+  scoped_ptr<ScopedAnimationFrameTask> raf_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerAnimatorCollection);
 };