Prefer ScopedNestableTaskAllower over manual save/restore

content/browser/download/drag_download_file.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 "content/browser/download/drag_download_file.h"
 
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/message_loop.h"
 #include "content/browser/download/download_stats.h"
@@ skipping 205 matching lines @@
   // Only do the check on Windows where two threads are involved.
 #if defined(OS_WIN)
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 #endif
 }
 
 #if defined(OS_WIN)
 void DragDownloadFile::StartNestedMessageLoop() {
   AssertCurrentlyOnDragThread();
 
-  bool old_state = MessageLoop::current()->NestableTasksAllowed();
-  MessageLoop::current()->SetNestableTasksAllowed(true);
+  MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
   is_running_nested_message_loop_ = true;
   MessageLoop::current()->Run();
-  MessageLoop::current()->SetNestableTasksAllowed(old_state);
+  DCHECK(!is_running_nested_message_loop_);
 }
 
 void DragDownloadFile::QuitNestedMessageLoop() {
   AssertCurrentlyOnDragThread();
 
   if (is_running_nested_message_loop_) {
     is_running_nested_message_loop_ = false;
     MessageLoop::current()->Quit();
   }
 }
 #endif