ui/base: Move message_box_win.{h,cc} to ui/base/win.

ui/base/win/message_box_win.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// 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_MESSAGE_BOX_WIN_H_
-#define UI_BASE_MESSAGE_BOX_WIN_H_
+#ifndef UI_BASE_WIN_MESSAGE_BOX_WIN_H_
+#define UI_BASE_WIN_MESSAGE_BOX_WIN_H_
 #pragma once
 
 #include <windows.h>
 
 #include "base/string16.h"
 #include "ui/base/ui_export.h"
 
 namespace ui {
 
 // A wrapper around Windows' MessageBox function. Using a Chrome specific
 // MessageBox function allows us to control certain RTL locale flags so that
 // callers don't have to worry about adding these flags when running in a
 // right-to-left locale.
 UI_EXPORT int MessageBox(HWND hwnd,
                          const string16& text,
                          const string16& caption,
                          UINT flags);
 
 }  // namespace ui
 
-#endif  // UI_BASE_MESSAGE_BOX_WIN_H_
+#endif  // UI_BASE_WIN_MESSAGE_BOX_WIN_H_