Prefer ScopedNestableTaskAllower over manual save/restore

chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc

Index: chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc
diff --git a/chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc b/chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc
index 795b9672025fc6e732cb8569ec8ba41209a52fd3..ab1a843353de93e1ba10d887708f4f71f27d5350 100644
--- a/chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc
+++ b/chrome/browser/ui/views/tab_contents/native_tab_contents_view_aura.cc
@@ -211,11 +211,12 @@ void NativeTabContentsViewAura::StartDragging(const WebDropData& drop_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);
-  int result_op = aura::client::GetDragDropClient()->StartDragAndDrop(
-      data, ConvertFromWeb(ops));
-  MessageLoop::current()->SetNestableTasksAllowed(old_state);
+  int result_op = 0;
+  {
+    MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
+    result_op = aura::client::GetDragDropClient()->StartDragAndDrop(

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

nit: Does this actually induce a nested message loop?

If so, it might be good to make that much more apparent in the underlying code,
as the code needs to be re-entrant.

I tried to look at what I *thought* was the code... but it was not immediately
clear when/how it created a sub-message loop.

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

sky will be the best person to comment here.  But it looks like the message loop
is created at ash/drag_drop/drag_drop_controller.cc:54, where messages are
dispatched back to the host framework.

[jar (doing other things), 2012/02/14 01:51:43]

Sky@

Do you think this is as close as you can get to the running of the nested
message loops?

Thanks,

Jim

On 2012/02/13 17:44:26, dhollowa wrote:

[sky, 2012/02/14 04:45:05]

DragDropController::StartDragAndDrop is closer (in ash/drag_drop).

[dhollowa, 2012/02/14 05:42:20]

Shall I move the scoper there then?  Or would you like to handle it?

+        data, ConvertFromWeb(ops));
+  }
 
   EndDrag(ConvertToWeb(result_op));
   GetWebContents()->GetRenderViewHost()->DragSourceSystemDragEnded();