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

ash/common/shelf/wm_shelf.h

Index: ash/common/shelf/wm_shelf.h
diff --git a/ash/common/shelf/wm_shelf.h b/ash/common/shelf/wm_shelf.h
index ee88e94b1525b44d9b1dd9bcec0e70e3596a4705..5e9aed6a7b8fef86aa711a3fff249205a98a408b 100644
--- a/ash/common/shelf/wm_shelf.h
+++ b/ash/common/shelf/wm_shelf.h
@@ -22,6 +22,7 @@ class GestureEvent;
 
 namespace ash {
 
+enum class AnimationChangeType;
 class ShelfBezelEventHandler;
 class ShelfLayoutManager;
 class ShelfLayoutManagerTest;
@@ -146,7 +147,7 @@ class ASH_EXPORT WmShelf : public ShelfLayoutManagerObserver {
   void WillChangeVisibilityState(ShelfVisibilityState new_state) override;
   void OnAutoHideStateChanged(ShelfAutoHideState new_state) override;
   void OnBackgroundUpdated(ShelfBackgroundType background_type,
-                           BackgroundAnimatorChangeType change_type) override;
+                           AnimationChangeType change_type) override;
 
  private:
   class AutoHideEventHandler;