Add missing IWYU message_loop.h includes.

media/remoting/demuxer_stream_adapter_unittest.cc

 // Copyright 2016 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 "media/remoting/demuxer_stream_adapter.h"
 
 #include <memory>
 #include <vector>
 
 #include "base/callback_helpers.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "media/base/decoder_buffer.h"
 #include "media/base/demuxer_stream.h"
 #include "media/remoting/fake_media_resource.h"
 #include "media/remoting/fake_remoter.h"
 #include "media/remoting/proto_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using testing::_;
@@ skipping 268 matching lines @@
   data_stream_sender_.reset();
   RunPendingTasks();  // Allow notification from mojo to propagate.
 
   demuxer_stream_adapter_->TakeErrors(&errors);
   ASSERT_EQ(1u, errors.size());
   EXPECT_EQ(MOJO_PIPE_ERROR, errors[0]);
 }
 
 }  // namesapce remoting
 }  // namespace media