Change SingletonHwnd to be based on WindowImpl.

ui/base/win/singleton_hwnd.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_BASE_WIN_SINGLETON_HWND_H_
 #define UI_BASE_WIN_SINGLETON_HWND_H_
 #pragma once
 
 #include <windows.h>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/observer_list.h"
+#include "ui/base/win/window_impl.h"
 
 template<typename T> struct DefaultSingletonTraits;
 
 namespace ui {
 
 // Singleton message-only HWND that allows interested clients to receive WM_*
 // notifications.
-class SingletonHwnd {
+class SingletonHwnd : public WindowImpl {
  public:
   static SingletonHwnd* GetInstance();
 
   // Observer interface for receiving Windows WM_* notifications.
   class Observer {
    public:
     virtual void OnWndProc(HWND hwnd,
                            UINT message,
                            WPARAM wparam,
                            LPARAM lparam) = 0;
   };
 
   // Add/remove observer to receive WM_* notifications.
   void AddObserver(Observer* observer);
   void RemoveObserver(Observer* observer);
 
   // Windows callback for WM_* notifications.
-  void OnWndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
+  virtual BOOL ProcessWindowMessage(HWND window,
+                                    UINT message,
+                                    WPARAM wparam,
+                                    LPARAM lparam,
+                                    LRESULT& result,
+                                    DWORD msg_map_id) OVERRIDE;
 
  private:
   friend struct DefaultSingletonTraits<SingletonHwnd>;
 
   SingletonHwnd();
   ~SingletonHwnd();
 
-  // Listener HWND for WM_* notifications.
-  HWND listener_window_;
-
   // List of registered observers.
   ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(SingletonHwnd);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_WIN_SINGLETON_HWND_H_