Prefer ScopedNestableTaskAllower over manual save/restore

chrome/browser/ui/views/tab_contents/tab_contents_drag_win.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/tab_contents/tab_contents_drag_win.h"
 
 #include <windows.h>
 
 #include <string>
 
@@ skipping 294 matching lines @@
   }
 
   // Set drag image.
   if (!image.isNull()) {
     drag_utils::SetDragImageOnDataObject(
         image, gfx::Size(image.width(), image.height()), image_offset, &data);
   }
 
   // We need to enable recursive tasks on the message loop so we can get
   // updates while in the system DoDragDrop loop.
-  bool old_state = MessageLoop::current()->NestableTasksAllowed();
-  MessageLoop::current()->SetNestableTasksAllowed(true);
   DWORD effect;
-  DoDragDrop(ui::OSExchangeDataProviderWin::GetIDataObject(data), drag_source_,
-             web_drag_utils_win::WebDragOpMaskToWinDragOpMask(ops), &effect);
-  MessageLoop::current()->SetNestableTasksAllowed(old_state);
+  {
+    MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
+    DoDragDrop(ui::OSExchangeDataProviderWin::GetIDataObject(data),
+               drag_source_,
+               web_drag_utils_win::WebDragOpMaskToWinDragOpMask(ops),
+               &effect);
+  }
 
   // This works because WebDragSource::OnDragSourceDrop uses PostTask to
   // dispatch the actual event.
   drag_source_->set_effect(effect);
 }
 
 void TabContentsDragWin::EndDragging(bool restore_suspended_state) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   if (drag_ended_)
@@ skipping 39 matching lines @@
 void TabContentsDragWin::OnDataObjectDisposed() {
   DCHECK(drag_drop_thread_id_ == base::PlatformThread::CurrentId());
 
   // The drag-and-drop thread is only closed after OLE is done with
   // DataObjectImpl.
   BrowserThread::PostTask(
       BrowserThread::UI,
       FROM_HERE,
       base::Bind(&TabContentsDragWin::CloseThread, this));
 }