Reland of "Apply Shelf/Dock opacity animations for the Material Design style."

ash/common/shelf/wm_shelf_observer.h

 // Copyright 2016 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_WM_SHELF_OBSERVER_H_
 #define ASH_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/shelf/shelf_types.h"
 #include "ash/common/wm/background_animator.h"
 
 namespace ash {
 
 // Used to observe changes to the shelf.
 class ASH_EXPORT WmShelfObserver {
  public:
-  virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
-                                   BackgroundAnimatorChangeType change_type) {}
+  virtual void OnBackgroundTypeChanged(
+      ShelfBackgroundType background_type,
+      BackgroundAnimatorChangeType change_type) {}
   virtual void WillChangeVisibilityState(ShelfVisibilityState new_state) {}
   virtual void OnAutoHideStateChanged(ShelfAutoHideState new_state) {}
   virtual void OnShelfIconPositionsChanged() {}
 
  protected:
   virtual ~WmShelfObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_WM_SHELF_OBSERVER_H_