Refactors WindowResizers to use ash/wm/common

ash/wm/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_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 #define ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 
 #include "ash/ash_export.h"
-// TODO(sky): refactor into common.
 #include "ash/wm/common/background_animator.h"
 #include "ash/wm/common/shelf/wm_shelf_types.h"
 
 namespace ash {
 namespace wm {
 
 class WmWindow;
 
 // Used to observe changes to the shelf.
 class ASH_EXPORT WmShelfObserver {
  public:
   virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
                                    BackgroundAnimatorChangeType change_type) {}
+  virtual void WillChangeVisibilityState(ShelfVisibilityState new_state) {}
+  virtual void OnShelfIconPositionsChanged() {}
 
  protected:
   virtual ~WmShelfObserver() {}
 };
 
 }  // namespace wm
 }  // namespace ash
 
 #endif  // ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_