[ash-md] Remove the number of animators used for the Shelf animations.

ash/common/shelf/shelf_background_animator_observer.h

Index: ash/common/shelf/shelf_background_animator_observer.h
diff --git a/ash/common/shelf/shelf_background_animator_observer.h b/ash/common/shelf/shelf_background_animator_observer.h
index a90b30867fc020bc15dbfbf5297cc4df990fa35c..a2a021d69ce198e51070aaa7a35be6733dd4cc42 100644
--- a/ash/common/shelf/shelf_background_animator_observer.h
+++ b/ash/common/shelf/shelf_background_animator_observer.h
@@ -12,8 +12,8 @@ namespace ash {
 // Observer for the ShelfBackgroundAnimator class.
 class ASH_EXPORT ShelfBackgroundAnimatorObserver {
  public:
-  // Called when the Shelf's opaque background should be updated.
-  virtual void UpdateShelfOpaqueBackground(int alpha) {}
+  // Called when the Shelf's background should be updated.
+  virtual void UpdateShelfBackground(int alpha) {}
 
   // Called when the Shelf item (aka button) backgrounds should be updated.
   virtual void UpdateShelfItemBackground(int alpha) {}