Split the singleton hwnd from screen_compatible_dc_win.cc.

ui/base/win/singleton_hwnd.h

Index: ui/base/win/singleton_hwnd.h
===================================================================
--- ui/base/win/singleton_hwnd.h	(revision 0)
+++ ui/base/win/singleton_hwnd.h	(revision 0)
@@ -0,0 +1,49 @@
+// 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/memory/singleton.h"
+
+namespace ui {
+
+typedef base::Callback<void(HWND, UINT, WPARAM, LPARAM)> WndProcCallback;
+
+// Singleton HWND that allows interested clients to receive WM_* notifications.
+class SingletonHwnd {
+ public:
+  // Singleton getter.
+  static SingletonHwnd* GetInstance();
+
+  // Registers a listener callback for WM_* notifications.
+  void RegisterListener(WndProcCallback& callback);
+
+  // Windows callback for WM_* notifications.
+  void OnWndProc(HWND hwnd, UINT message, WPARAM wparam, LPARAM lparam);
+
+ private:
+  SingletonHwnd();
+  ~SingletonHwnd();
+
+  // Listener HWND for WM_* notifications.
+  HWND listener_window_;
+
+  // List of registered listener callbacks.
+  std::vector<WndProcCallback> listeners_;
+
+  friend struct DefaultSingletonTraits<SingletonHwnd>;
+
+  DISALLOW_COPY_AND_ASSIGN(SingletonHwnd);
+};
+
+}  // namespace ui
+
+#endif  // UI_BASE_WIN_SINGLETON_HWND_H_