Cleanup: Remove unneeded forward declarations from chrome/browser/chromeos.

chrome/browser/chromeos/login/screen_locker_tester.h

 // Copyright (c) 2011 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 CHROME_BROWSER_CHROMEOS_LOGIN_SCREEN_LOCKER_TESTER_H_
 #define CHROME_BROWSER_CHROMEOS_LOGIN_SCREEN_LOCKER_TESTER_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 
 namespace views {
-class Button;
 class Textfield;
 class Widget;
 }  // namespace views
 
 namespace chromeos {
 
 class ScreenLocker;
 class ScreenLockerViews;
 
 namespace test {
@@ skipping 37 matching lines @@
   views::Textfield* GetPasswordField() const;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenLockerTester);
 };
 
 }  // namespace test
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_LOGIN_SCREEN_LOCKER_TESTER_H_