Add missing IWYU message_loop.h includes.

ppapi/proxy/plugin_globals.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 "ppapi/proxy/plugin_globals.h"
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/task_runner.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "ipc/ipc_message.h"
 #include "ipc/ipc_sender.h"
 #include "ppapi/proxy/plugin_dispatcher.h"
 #include "ppapi/proxy/plugin_message_filter.h"
 #include "ppapi/proxy/plugin_proxy_delegate.h"
 #include "ppapi/proxy/ppapi_messages.h"
 #include "ppapi/proxy/ppb_message_loop_proxy.h"
@@ skipping 210 matching lines @@
     ppapi::proxy::PluginMessageFilter* plugin_filter) {
   plugin_filter->AddResourceMessageFilter(udp_socket_filter_.get());
 }
 
 bool PluginGlobals::IsPluginGlobals() const {
   return true;
 }
 
 }  // namespace proxy
 }  // namespace ppapi