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

ui/aura/root_window.h

 // Copyright (c) 2012 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 UI_AURA_ROOT_WINDOW_H_
 #define UI_AURA_ROOT_WINDOW_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 263 matching lines @@
   // |mouse_moved_handler_|.
   void DispatchMouseEnterOrExit(const ui::MouseEvent& event,
                                 ui::EventType type);
 
   void ProcessEvent(Window* target, ui::Event* event);
 
   bool ProcessGestures(ui::GestureRecognizer::Gestures* gestures);
 
   // Called when a Window is attached or detached from the RootWindow.
   void OnWindowAddedToRootWindow(Window* window);
-  void OnWindowRemovedFromRootWindow(Window* window, RootWindow* new_root);
+  void OnWindowRemovedFromRootWindow(Window* window, Window* new_root);
 
   // Called when a window becomes invisible, either by being removed
   // from root window hierarchy, via SetVisible(false) or being destroyed.
   // |reason| specifies what triggered the hiding.
   void OnWindowHidden(Window* invisible, WindowHiddenReason reason);
 
   // Cleans up the gesture recognizer for all windows in |window| (including
   // |window| itself).
   void CleanupGestureRecognizerState(Window* window);
 
@@ skipping 110 matching lines @@
   base::WeakPtrFactory<RootWindow> held_event_factory_;
 
   base::WeakPtrFactory<RootWindow> repostable_event_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RootWindow);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_ROOT_WINDOW_H_