Add missing IWYU message_loop.h includes.

remoting/host/setup/start_host_main.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 "remoting/host/setup/start_host_main.h"
 
 #include <stddef.h>
 #include <stdio.h>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/threading/thread.h"
 #include "build/build_config.h"
 #include "net/url_request/url_fetcher.h"
 #include "net/url_request/url_request_context_getter.h"
 #include "remoting/base/logging.h"
 #include "remoting/base/oauth_helper.h"
@@ skipping 215 matching lines @@
   // IO thread.
   host_starter.reset();
   url_request_context_getter = nullptr;
 
   io_thread.Stop();
 
   return g_started ? 0 : 1;
 }
 
 }  // namespace remoting