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

ash/common/shelf/shelf_layout_manager_observer.h

Index: ash/common/shelf/shelf_layout_manager_observer.h
diff --git a/ash/common/shelf/shelf_layout_manager_observer.h b/ash/common/shelf/shelf_layout_manager_observer.h
index fd9711b489cf51de8575effab0094d9bee4d48f7..9437a8c59418af3ecd65935e56acfa6d2ae1165f 100644
--- a/ash/common/shelf/shelf_layout_manager_observer.h
+++ b/ash/common/shelf/shelf_layout_manager_observer.h
@@ -6,9 +6,13 @@
 #define ASH_COMMON_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_
 
 #include "ash/ash_export.h"
-#include "ash/common/wm/background_animator.h"
+#include "ash/common/shelf/shelf_background_animator.h"
 #include "ash/public/cpp/shelf_types.h"
 
+namespace gfx {
+enum class AnimationChangeType;
+}  // namespace gfx
+
 namespace ash {
 
 class ASH_EXPORT ShelfLayoutManagerObserver {
@@ -26,7 +30,7 @@ class ASH_EXPORT ShelfLayoutManagerObserver {
 
   // Called when shelf background animation is started.
   virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
-                                   BackgroundAnimatorChangeType change_type) {}
+                                   gfx::AnimationChangeType change_type) {}
 };
 
 }  // namespace ash