Prefer ScopedNestableTaskAllower over manual save/restore

ppapi/proxy/ppb_testing_proxy.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/ppb_testing_proxy.h"
 
 #include "base/message_loop.h"
 #include "ppapi/c/dev/ppb_testing_dev.h"
 #include "ppapi/proxy/enter_proxy.h"
 #include "ppapi/proxy/plugin_dispatcher.h"
@@ skipping 32 matching lines @@
     return PP_FALSE;
 
   PP_Bool result = PP_FALSE;
   dispatcher->Send(new PpapiHostMsg_PPBTesting_ReadImageData(
       API_ID_PPB_TESTING, graphics_2d_object->host_resource(),
       image_object->host_resource(), *top_left, &result));
   return result;
 }
 
 void RunMessageLoop(PP_Instance instance) {
-  bool old_state = MessageLoop::current()->NestableTasksAllowed();
-  MessageLoop::current()->SetNestableTasksAllowed(true);
+  MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
   MessageLoop::current()->Run();
-  MessageLoop::current()->SetNestableTasksAllowed(old_state);
 }
 
 void QuitMessageLoop(PP_Instance instance) {
   MessageLoop::current()->QuitNow();
 }
 
 uint32_t GetLiveObjectsForInstance(PP_Instance instance_id) {
   PluginDispatcher* dispatcher = PluginDispatcher::GetForInstance(instance_id);
   if (!dispatcher)
     return static_cast<uint32_t>(-1);
@@ skipping 122 matching lines @@
     PP_Instance instance,
     const InputEventData& input_event) {
   scoped_refptr<PPB_InputEvent_Shared> input_event_impl(
       new PPB_InputEvent_Shared(OBJECT_IS_PROXY, instance, input_event));
   ppb_testing_impl_->SimulateInputEvent(instance,
                                         input_event_impl->pp_resource());
 }
 
 }  // namespace proxy
 }  // namespace ppapi