Fix another d&d crash that happens when the tab contents

chrome/browser/tab_contents/web_drag_source.h

 // Copyright (c) 2006-2008 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 CHROME_BROWSER_TAB_CONTENTS_WEB_DRAG_SOURCE_H_
 #define CHROME_BROWSER_TAB_CONTENTS_WEB_DRAG_SOURCE_H_
 
 #include "base/basictypes.h"
 #include "base/gfx/native_widget_types.h"
 #include "base/gfx/point.h"
+#include "chrome/common/notification_observer.h"
+#include "chrome/common/notification_registrar.h"
 
 // TODO(port): Port this file.
 #if defined(OS_WIN)
 #include "base/base_drag_source.h"
 #else
 #include "chrome/common/temp_scaffolding_stubs.h"
 #endif
 
 class RenderViewHost;
+class TabContents;
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // WebDragSource
 //
 //  An IDropSource implementation for a TabContents. Handles notifications sent
 //  by an active drag-drop operation as the user mouses over other drop targets
 //  on their system. This object tells Windows whether or not the drag should
 //  continue, and supplies the appropriate cursors.
 //
-class WebDragSource : public BaseDragSource {
+class WebDragSource : public BaseDragSource,
+                      public NotificationObserver {
  public:
-  // Create a new DragSource for a given HWND and RenderViewHost.
-  WebDragSource(gfx::NativeWindow source_wnd, RenderViewHost* render_view_host);
+  // Create a new DragSource for a given HWND and TabContents.
+  WebDragSource(gfx::NativeWindow source_wnd, TabContents* tab_contents);
   virtual ~WebDragSource() { }
 
+  // NotificationObserver implementation.
+  virtual void Observe(NotificationType type,
+                       const NotificationSource& source,
+                       const NotificationDetails& details);
+
  protected:
   // BaseDragSource
   virtual void OnDragSourceCancel();
   virtual void OnDragSourceDrop();
   virtual void OnDragSourceMove();
 
  private:
   // Cannot construct thusly.
   WebDragSource();
 
   // Keep a reference to the window so we can translate the cursor position.
   gfx::NativeWindow source_wnd_;
 
   // We use this as a channel to the renderer to tell it about various drag
   // drop events that it needs to know about (such as when a drag operation it
   // initiated terminates).
   RenderViewHost* render_view_host_;
 
+  NotificationRegistrar registrar_;
+
   DISALLOW_COPY_AND_ASSIGN(WebDragSource);
 };
 
 #endif  // #ifndef CHROME_BROWSER_TAB_CONTENTS_WEB_DRAG_SOURCE_H_