Add missing IWYU message_loop.h includes.

ppapi/nacl_irt/irt_ppapi.cc

 // Copyright 2014 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 "build/build_config.h"
 
 #include <stdint.h>
 
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/threading/thread.h"
 #include "ipc/ipc_logging.h"
 #include "ppapi/nacl_irt/irt_interfaces.h"
 #include "ppapi/nacl_irt/irt_ppapi.h"
 #include "ppapi/nacl_irt/plugin_startup.h"
 #include "ppapi/nacl_irt/ppapi_dispatcher.h"
 #include "ppapi/nacl_irt/public/irt_ppapi.h"
 #include "ppapi/proxy/plugin_globals.h"
 #include "ppapi/shared_impl/ppb_audio_shared.h"
@@ skipping 35 matching lines @@
 }
 
 const void* PPP_GetInterface(const char* interface_name) {
   return g_pp_functions.PPP_GetInterface(interface_name);
 }
 
 const struct nacl_irt_ppapihook nacl_irt_ppapihook = {
   irt_ppapi_start,
   PpapiPluginRegisterThreadCreator,
 };