Add missing IWYU message_loop.h includes.

chromecast/media/cma/base/multi_demuxer_stream_adapter_unittest.cc

 // Copyright 2015 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 <memory>
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.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/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "chromecast/media/cma/base/balanced_media_task_runner_factory.h"
 #include "chromecast/media/cma/base/decoder_buffer_base.h"
 #include "chromecast/media/cma/base/demuxer_stream_adapter.h"
 #include "chromecast/media/cma/base/demuxer_stream_for_test.h"
 #include "chromecast/public/media/cast_decoder_buffer.h"
@@ skipping 139 matching lines @@
   total_expected_frames_ = frame_count_short + frame_count_long;
 
   std::unique_ptr<base::MessageLoop> message_loop(new base::MessageLoop());
   message_loop->task_runner()->PostTask(
       FROM_HERE, base::Bind(&MultiDemuxerStreamAdaptersTest::Start,
                             base::Unretained(this)));
   base::RunLoop().Run();
 }
 }  // namespace media
 }  // namespace chromecast