CC Animations: Make ui::LayerAnimator a LayerAnimationEventObserver (instead of ui::Layer)

ui/compositor/layer_animation_delegate.h

Index: ui/compositor/layer_animation_delegate.h
diff --git a/ui/compositor/layer_animation_delegate.h b/ui/compositor/layer_animation_delegate.h
index 0643f35ae0bcb45216da998c408897ec23533312..cc83f43d5364be081441defbc0995d934735d469 100644
--- a/ui/compositor/layer_animation_delegate.h
+++ b/ui/compositor/layer_animation_delegate.h
@@ -12,6 +12,10 @@
 #include "ui/gfx/geometry/rect.h"
 #include "ui/gfx/transform.h"
 
+namespace cc {
+class Layer;
+}
+
 namespace ui {
 
 class LayerAnimatorCollection;
@@ -38,6 +42,7 @@ class COMPOSITOR_EXPORT LayerAnimationDelegate {
   virtual void AddThreadedAnimation(scoped_ptr<cc::Animation> animation) = 0;
   virtual void RemoveThreadedAnimation(int animation_id) = 0;
   virtual LayerAnimatorCollection* GetLayerAnimatorCollection() = 0;
+  virtual cc::Layer* GetCcLayer() const = 0;
 
  protected:
   virtual ~LayerAnimationDelegate() {}