Fix the crash that could occur when the window is closed while web contents drag is in progress.

content/browser/web_contents/web_contents_drag_win.h

 // 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.
 
 #ifndef CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_DRAG_WIN_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_DRAG_WIN_H_
 
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/memory/ref_counted.h"
@@ skipping 49 matching lines @@
  private:
   // Called on either UI thread or drag-and-drop thread.
   void PrepareDragForDownload(const WebDropData& drop_data,
                               ui::OSExchangeData* data,
                               const GURL& page_url,
                               const std::string& page_encoding);
   void PrepareDragForFileContents(const WebDropData& drop_data,
                                   ui::OSExchangeData* data);
   void PrepareDragForUrl(const WebDropData& drop_data,
                          ui::OSExchangeData* data);
-  void DoDragging(const WebDropData& drop_data,
+  // Returns false if the source window becomes invalid when the drag ends.
+  // This could happens when the window gets destroyed when the drag is still in

[Ben Goodger (Google), 2012/09/27 16:05:20]

happen

+  // progress. No further processing should be done beyond this return point
+  // because the instance has been disposed.

[Ben Goodger (Google), 2012/09/27 16:05:20]

destroyed.

+  bool DoDragging(const WebDropData& drop_data,
                   WebKit::WebDragOperationsMask ops,
                   const GURL& page_url,
                   const std::string& page_encoding,
                   const gfx::ImageSkia& image,
                   const gfx::Point& image_offset);
 
   // Called on drag-and-drop thread.
   void StartBackgroundDragging(const WebDropData& drop_data,
                                WebKit::WebDragOperationsMask ops,
                                const GURL& page_url,
@@ skipping 24 matching lines @@
 
   // The flag to guard that EndDragging is not called twice.
   bool drag_ended_;
 
   base::Callback<void()> drag_end_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsDragWin);
 };
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_WEB_CONTENTS_DRAG_WIN_H_