Add missing IWYU message_loop.h includes.

chrome/browser/media_galleries/fileapi/itunes_file_util_unittest.cc

 // Copyright 2013 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/media_galleries/fileapi/itunes_file_util.h"
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/bind_helpers.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/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "chrome/browser/media_galleries/fileapi/itunes_data_provider.h"
 #include "chrome/browser/media_galleries/fileapi/media_file_system_backend.h"
 #include "chrome/browser/media_galleries/fileapi/media_path_filter.h"
 #include "chrome/browser/media_galleries/imported_media_gallery_registry.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 317 matching lines @@
   completed = false;
   ReadDirectoryTestHelper(operation_runner(), url, &contents, &completed);
   ASSERT_TRUE(completed);
   ASSERT_EQ(1u, contents.size());
   EXPECT_FALSE(contents.front().is_directory);
   EXPECT_EQ(base::FilePath().AppendASCII("baz.ogg").value(),
             contents.front().name);
 }
 
 }  // namespace itunes