Add missing IWYU message_loop.h includes.

media/cast/test/sender.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.
 
 // Test application that simulates a cast sender - Data can be either generated
 // or read from a file.
 
 #include <stdint.h>
 
 #include <memory>
 #include <queue>
 #include <utility>
 
 #include "base/at_exit.h"
 #include "base/base_paths.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/threading/thread.h"
 #include "base/time/default_tick_clock.h"
 #include "base/values.h"
 #include "media/base/media.h"
 #include "media/base/video_frame.h"
 #include "media/cast/cast_config.h"
@@ skipping 318 matching lines @@
       FROM_HERE, base::Bind(&media::cast::CastSender::InitializeAudio,
                             base::Unretained(cast_sender.get()), audio_config,
                             base::Bind(&QuitLoopOnInitializationResult)));
   base::RunLoop().Run();  // Wait for audio initialization.
 
   fake_media_source->Start(cast_sender->audio_frame_input(),
                            cast_sender->video_frame_input());
   base::RunLoop().Run();
   return 0;
 }