Added LayerAnimationObserver::OnLayerAnimationStarted() notification.

ui/compositor/layer_animation_observer.h

 // Copyright (c) 2012 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 UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_
 #define UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_
 
 #include <map>
 #include <set>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/compositor/layer_animation_element.h"
 
 namespace ui {
 
 class LayerAnimationSequence;
 class ScopedLayerAnimationSettings;
 class ImplicitAnimationObserver;
 
 // LayerAnimationObservers are notified when animations complete.
 class COMPOSITOR_EXPORT LayerAnimationObserver  {
  public:
+  // Called when the |sequence| starts.
+  virtual void OnLayerAnimationStarted(LayerAnimationSequence* sequence);
+
   // Called when the |sequence| ends. Not called if |sequence| is aborted.
   virtual void OnLayerAnimationEnded(
       LayerAnimationSequence* sequence) = 0;
 
   // Called if |sequence| is aborted for any reason. Should never do anything
   // that may cause another animation to be started.
   virtual void OnLayerAnimationAborted(
       LayerAnimationSequence* sequence) = 0;
 
   // Called when the animation is scheduled.
@@ skipping 108 matching lines @@
                    AnimationStatus> PropertyAnimationStatusMap;
   PropertyAnimationStatusMap property_animation_status_;
 
   // True if OnLayerAnimationScheduled() has been called at least once.
   bool first_sequence_scheduled_;
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_LAYER_ANIMATION_OBSERVER_H_