Add missing IWYU message_loop.h includes.

components/storage_monitor/storage_monitor_chromeos_unittest.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 "components/storage_monitor/storage_monitor_chromeos.h"
 
 #include <stdint.h>
 
 #include <memory>
 #include <utility>
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chromeos/disks/mock_disk_mount_manager.h"
 #include "components/storage_monitor/mock_removable_storage_observer.h"
 #include "components/storage_monitor/removable_device_constants.h"
 #include "components/storage_monitor/storage_info.h"
 #include "components/storage_monitor/test_media_transfer_protocol_manager_chromeos.h"
 #include "components/storage_monitor/test_storage_monitor.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/test/test_browser_thread_bundle.h"
@@ skipping 524 matching lines @@
                         base::Bind(&StorageMonitorCrosTest::EjectNotify,
                                    base::Unretained(this)));
   base::RunLoop().RunUntilIdle();
 
   EXPECT_EQ(StorageMonitor::EJECT_OK, status_);
 }
 
 }  // namespace
 
 }  // namespace storage_monitor