Add missing IWYU message_loop.h includes.

chromecast/media/cma/base/buffering_frame_provider_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 "chromecast/media/cma/base/buffering_frame_provider.h"
 
 #include <stddef.h>
 
 #include <list>
 #include <memory>
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread.h"
 #include "base/time/time.h"
 #include "chromecast/media/cma/test/frame_generator_for_test.h"
 #include "chromecast/media/cma/test/mock_frame_consumer.h"
 #include "chromecast/media/cma/test/mock_frame_provider.h"
 #include "chromecast/public/media/cast_decoder_buffer.h"
 #include "media/base/audio_decoder_config.h"
 #include "media/base/decoder_buffer.h"
@@ skipping 152 matching lines @@
 
   std::unique_ptr<base::MessageLoop> message_loop(new base::MessageLoop());
   message_loop->task_runner()->PostTask(
       FROM_HERE,
       base::Bind(&BufferingFrameProviderTest::Start, base::Unretained(this)));
   base::RunLoop().Run();
 }
 
 }  // namespace media
 }  // namespace chromecast