Add missing IWYU message_loop.h includes.

media/audio/audio_low_latency_input_output_unittest.cc

 // Copyright (c) 2012 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 <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
 #include <memory>
 
 #include "base/bind.h"
 #include "base/environment.h"
 #include "base/files/file_util.h"
 #include "base/macros.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/synchronization/lock.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "build/build_config.h"
 #include "media/audio/audio_device_description.h"
 #include "media/audio/audio_device_info_accessor_for_tests.h"
@@ skipping 425 matching lines @@
   // should be synchronous and not post additional close tasks to
   // mocked the audio thread. Hence, there is no need to call
   // message_loop()->RunUntilIdle() after the Close() methods.
   aos->Close();
   ais->Close();
 }
 
 }  // namespace
 
 }  // namespace media