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

ash/root_window_settings.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_ROOT_WINDOW_SETTINGS_H_
 #define ASH_ROOT_WINDOW_SETTINGS_H_
 
 #include "ash/ash_export.h"
 #include "base/basictypes.h"
 
 namespace aura {
-class RootWindow;
+class Window;
 }
 
 namespace ash {
 namespace internal {
 
 class RootWindowController;
 
 // Per root window information should be stored here
 // instead of using plain aura root window property because
 // it can prevent mis-using on non root window.
 struct RootWindowSettings {
   RootWindowSettings();
 
   // Indicate if the window in the active workspace should
   // use the transparent "solo-window" header style.
   bool solo_window_header;
 
   // ID of the display associated with the root window.
   int64 display_id;
 
   // RootWindowController for the root window. This may be NULL
   // for the root window used for mirroring.
   RootWindowController* controller;
 };
 
 // Initializes and returns RootWindowSettings for |root|.
 // It is owned by the |root|.
-RootWindowSettings* InitRootWindowSettings(aura::RootWindow* root);
+RootWindowSettings* InitRootWindowSettings(aura::Window* root);
 
 // Returns the RootWindowSettings for |root|.
-ASH_EXPORT RootWindowSettings* GetRootWindowSettings(aura::RootWindow* root);
+ASH_EXPORT RootWindowSettings* GetRootWindowSettings(aura::Window* root);
 
 // const version of GetRootWindowSettings.
 ASH_EXPORT const RootWindowSettings*
-GetRootWindowSettings(const aura::RootWindow* root);
+GetRootWindowSettings(const aura::Window* root);
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_ROOT_WINDOW_SETTINGS_H_