Add missing IWYU message_loop.h includes.

chrome/browser/chromeos/login/lock/screen_locker_tester.cc

 // Copyright 2014 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.
 
 #include "chrome/browser/chromeos/login/lock/screen_locker_tester.h"
 
 #include <string>
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/chromeos/login/lock/screen_locker.h"
 #include "chrome/browser/chromeos/login/lock/webui_screen_locker.h"
 #include "chromeos/login/auth/auth_status_consumer.h"
 #include "chromeos/login/auth/fake_extended_authenticator.h"
 #include "chromeos/login/auth/stub_authenticator.h"
 #include "content/public/browser/render_frame_host.h"
@@ skipping 189 matching lines @@
       new FakeExtendedAuthenticator(ScreenLocker::screen_locker_, user_context);
 }
 
 }  // namespace test
 
 test::ScreenLockerTester* ScreenLocker::GetTester() {
   return new test::WebUIScreenLockerTester();
 }
 
 }  // namespace chromeos