Prefer ScopedNestableTaskAllower over manual save/restore

chrome/browser/ui/views/simple_message_box_views.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 "chrome/browser/ui/views/simple_message_box_views.h"
 
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/simple_message_box.h"
 #include "chrome/browser/ui/dialog_style.h"
@@ skipping 44 matching lines @@
   // until we retrieve the user response..
   scoped_refptr<SimpleMessageBoxViews> dialog =
       new SimpleMessageBoxViews(parent_window, DIALOG_YES_NO, title, message);
 
   // Make sure Chrome doesn't attempt to shut down with the dialog up.
   g_browser_process->AddRefModule();
 
 #if defined(USE_AURA)
   aura::client::GetDispatcherClient()->RunWithDispatcher(dialog, true);
 #else
-  bool old_state = MessageLoopForUI::current()->NestableTasksAllowed();
-  MessageLoopForUI::current()->SetNestableTasksAllowed(true);
-  MessageLoopForUI::current()->RunWithDispatcher(dialog);
-  MessageLoopForUI::current()->SetNestableTasksAllowed(old_state);
+  {
+    MessageLoop::ScopedNestableTaskAllower allow(MessageLoopForUI::current());
+    MessageLoopForUI::current()->RunWithDispatcher(dialog);
+  }
 #endif
 
   g_browser_process->ReleaseModule();

[jar (doing other things), 2012/02/11 03:24:38]

nit/curious question: What are the potential side effects of this
ReleaseModule()?  How much destruction can take place, or is it all just posted
events, and that is why it is safe to do now (and not while we're in a
sub-loop)?

[dhollowa, 2012/02/13 17:44:26]

This is meant to match the |AddRefModule| at line 60, a guard against shutdown
with the dialog up.  If this is the last "release" then quit messages are posted
to the IO thread and the main UI thread is "Quit".  This seems ok.

 
   return dialog->Accepted();
 }
 
 bool SimpleMessageBoxViews::Cancel() {
   disposition_ = DISPOSITION_CANCEL;
   return true;
 }
 
 bool SimpleMessageBoxViews::Accept() {
@@ skipping 79 matching lines @@
   if (disposition_ == DISPOSITION_UNKNOWN)
     return base::MessagePumpDispatcher::EVENT_PROCESSED;
   return base::MessagePumpDispatcher::EVENT_QUIT;
 }
 #else
 bool SimpleMessageBoxViews::Dispatch(GdkEvent* event) {
   gtk_main_do_event(event);
   return disposition_ == DISPOSITION_UNKNOWN;
 }
 #endif