Add missing IWYU message_loop.h includes.

chrome/browser/policy/policy_browsertest.cc

 // 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.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
 #include <memory>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "ash/accelerators/accelerator_controller_delegate_aura.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/scoped_feature_list.h"
 #include "base/test/test_file_util.h"
 #include "base/threading/sequenced_worker_pool.h"
@@ skipping 4457 matching lines @@
 
   SetEmptyPolicy();
   // Policy not set.
   CheckSystemTimezoneAutomaticDetectionPolicyUnset();
   EXPECT_TRUE(CheckResolveTimezoneByGeolocation(true, false));
   EXPECT_TRUE(manager->TimeZoneResolverShouldBeRunningForTests());
 }
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace policy