Make GetRootWindow() return a Window instead of a RootWindow.

ash/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_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_
 #define ASH_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/shelf/shelf_types.h"
 
 namespace aura {
-class RootWindow;
+class Window;
 }
 
 namespace ash {
 
 class ASH_EXPORT ShelfLayoutManagerObserver {
  public:
   virtual ~ShelfLayoutManagerObserver() {}
 
   // Called when the target ShelfLayoutManager will be deleted.
   virtual void WillDeleteShelf() {}
 
   // 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 the auto hide behavior is changed.
-  virtual void OnAutoHideBehaviorChanged(aura::RootWindow* root_window,
+  virtual void OnAutoHideBehaviorChanged(aura::Window* root_window,
                                          ShelfAutoHideBehavior new_behavior) {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_LAYOUT_MANAGER_OBSERVER_H_