ash: Cleanup class/struct forward declarations

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/public/cpp/shelf_types.h"
 
-namespace aura {
-class Window;
-}
-
 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) {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_