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

ash/common/shelf/shelf_widget.h

Index: ash/common/shelf/shelf_widget.h
diff --git a/ash/common/shelf/shelf_widget.h b/ash/common/shelf/shelf_widget.h
index 995ef8ce17be269da93adfef3a72653eda4ec652..dac4c5f1edefc05eac5ea0e16bc833d2675ab296 100644
--- a/ash/common/shelf/shelf_widget.h
+++ b/ash/common/shelf/shelf_widget.h
@@ -21,6 +21,7 @@ class ApplicationDragAndDropHost;
 }
 
 namespace ash {
+enum class AnimationChangeType;
 class AppListButton;
 class FocusCycler;
 class ShelfLayoutManager;
@@ -46,7 +47,7 @@ class ASH_EXPORT ShelfWidget : public views::Widget,
 
   // Sets the shelf's background type.
   void SetPaintsBackground(ShelfBackgroundType background_type,
-                           BackgroundAnimatorChangeType change_type);
+                           AnimationChangeType change_type);
   ShelfBackgroundType GetBackgroundType() const;
 
   // Hide the shelf behind a black bar during e.g. a user transition when |hide|