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

ash/common/shelf/shelf_layout_manager_observer.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ASH_COMMON_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_
 #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 {
  public:
   virtual ~ShelfLayoutManagerObserver() {}
 
   // Called when the target ShelfLayoutManager will be deleted.
   virtual void WillDeleteShelfLayoutManager() {}
 
   // Called when the visibility change is scheduled.
   virtual void WillChangeVisibilityState(ShelfVisibilityState new_state) {}
 
   // Called when the auto hide state is changed.
   virtual void OnAutoHideStateChanged(ShelfAutoHideState new_state) {}
 
   // Called when shelf background animation is started.
   virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
-                                   BackgroundAnimatorChangeType change_type) {}
+                                   gfx::AnimationChangeType change_type) {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_