Prefer ScopedNestableTaskAllower over manual save/restore

chrome/browser/automation/automation_provider_win.cc

 // Copyright (c) 2011 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/automation/automation_provider.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/debug/trace_event.h"
 #include "base/json/json_reader.h"
@@ skipping 131 matching lines @@
       ui_controls::SendKeyPressNotifyWhenDone(
           window, ui::VKEY_ESCAPE,
           ((flags & ui::EF_CONTROL_DOWN) ==
            ui::EF_CONTROL_DOWN),
           ((flags & ui::EF_SHIFT_DOWN) ==
            ui::EF_SHIFT_DOWN),
           ((flags & ui::EF_ALT_DOWN) == ui::EF_ALT_DOWN),
           false,
           MessageLoop::QuitClosure());
       MessageLoopForUI* loop = MessageLoopForUI::current();
-      bool did_allow_task_nesting = loop->NestableTasksAllowed();
-      loop->SetNestableTasksAllowed(true);
+      MessageLoop::ScopedNestableTaskAllower allow(loop);
       views::AcceleratorHandler handler;

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

nit: although this mimics the existing code... IMO, we should construct the
handler outside of the scope of the nestable message loop, just so that we don't
accidentally(?) have any potential for running a nested loop (invisibly).

I'd suggest exchanging lines 152 and 153.

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

Done.

       loop->RunWithDispatcher(&handler);
-      loop->SetNestableTasksAllowed(did_allow_task_nesting);
     }
     SendMessage(top_level_hwnd, up_message, wparam_flags,
                 MAKELPARAM(end.x, end.y));
 
     MessageLoop::current()->PostTask(
         FROM_HERE, base::Bind(
             &InvokeCallbackLater,
             base::Bind(&WindowDragResponseCallback, this, reply_message)));
   } else {
     AutomationMsg_WindowDrag::WriteReplyParams(reply_message, false);
@@ skipping 237 matching lines @@
 void AutomationProvider::OnSetZoomLevel(int handle, int zoom_level) {
   if (tab_tracker_->ContainsHandle(handle)) {
     NavigationController* tab = tab_tracker_->GetResource(handle);
     if (tab->GetWebContents() && tab->GetWebContents()->GetRenderViewHost()) {
       RenderViewHost* host = tab->GetWebContents()->GetRenderViewHost();
       content::PageZoom zoom = static_cast<content::PageZoom>(zoom_level);
       host->Zoom(zoom);
     }
   }
 }