Add missing IWYU message_loop.h includes.

net/test/spawned_test_server/spawner_communicator.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 "net/test/spawned_test_server/spawner_communicator.h"
 
 #include <limits>
 #include <utility>
 
 #include "base/json/json_reader.h"
 #include "base/location.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/stringprintf.h"
 #include "base/supports_user_data.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "net/base/elements_upload_data_stream.h"
 #include "net/base/port_util.h"
@@ skipping 363 matching lines @@
   std::string server_return_data;
   int result_code;
   SendCommandAndWaitForResult("kill", "", &result_code, &server_return_data);
   Shutdown();
   if (OK != result_code || server_return_data != "killed")
     return false;
   return true;
 }
 
 }  // namespace net