Fix deadlock between UI thread and drag and drop thread on Windows.

content/browser/web_contents/web_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 "content/browser/web_contents/web_contents_drag_win.h"
 
 #include <windows.h>
 
 #include <string>
 
@@ skipping 343 matching lines @@
   HWND native_window = web_contents_->GetView()->GetNativeView();
 
   // We need to enable recursive tasks on the message loop so we can get
   // updates while in the system DoDragDrop loop.
   DWORD effect = DROPEFFECT_NONE;
   if (run_do_drag_drop) {
     // Keep a reference count such that |drag_source_| will not get deleted
     // if the contents view window is gone in the nested message loop invoked
     // from DoDragDrop.
     scoped_refptr<WebDragSource> retain_this(drag_source_);
+    drag_source_->set_data(&data);
+    data.SetInDragLoop(true);
 
     MessageLoop::ScopedNestableTaskAllower allow(MessageLoop::current());
     DoDragDrop(ui::OSExchangeDataProviderWin::GetIDataObject(data),
                drag_source_,
                WebDragOpMaskToWinDragOpMask(ops),
                &effect);
+    drag_source_->set_data(NULL);

[sky, 2013/04/26 22:10:22]

How do we know 'this' has been destroyed once the nested message loop unravels?

[dcheng, 2013/04/26 22:20:10]

Updated to the retained scoped_refptr on the stack.

   }
 
   // Bail out immediately if the contents view window is gone.
   if (!IsWindow(native_window))
     return false;
 
   // Normally, the drop and dragend events get dispatched in the system
   // DoDragDrop message loop so it'd be too late to set the effect to send back
   // to the renderer here. However, we use PostTask to delay the execution of
   // WebDragSource::OnDragSourceDrop, which means that the delayed dragend
@@ skipping 51 matching lines @@
       FROM_HERE,
       base::Bind(&WebContentsDragWin::CloseThread, this));
 }
 
 // static
 void WebContentsDragWin::DisableDragDropForTesting() {
   run_do_drag_drop = false;
 }
 
 }  // namespace content