Fix the issue that any tab/window closing hotkey will crash the Pepper Flash Fullscreen.

content/browser/renderer_host/render_widget_host_delegate.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_RENDER_WIDGET_HOST_DELEGATE_H_
 #define CONTENT_BROWSER_RENDER_WIDGET_HOST_DELEGATE_H_
 
 #include "content/common/content_export.h"
 
 namespace content {
 
+class RenderWidgetHostImpl;
 struct NativeWebKeyboardEvent;
 
 //
 // RenderWidgetHostDelegate
 //
 //  An interface implemented by an object interested in knowing about the state
 //  of the RenderWidgetHost.
 class CONTENT_EXPORT RenderWidgetHostDelegate {
  public:
+  // The RenderWidgetHost is going to be deleted.
+  virtual void RenderWidgetDeleted(RenderWidgetHostImpl* render_widget_host) {}
+
   // Callback to give the browser a chance to handle the specified keyboard
   // event before sending it to the renderer.
   // Returns true if the |event| was handled. Otherwise, if the |event| would
   // be handled in HandleKeyboardEvent() method as a normal keyboard shortcut,
   // |*is_keyboard_shortcut| should be set to true.
   virtual bool PreHandleKeyboardEvent(const NativeWebKeyboardEvent& event,
                                       bool* is_keyboard_shortcut);
 
   // Callback to inform the browser that the renderer did not process the
   // specified events. This gives an opportunity to the browser to process the
   // event (used for keyboard shortcuts).
   virtual void HandleKeyboardEvent(const NativeWebKeyboardEvent& event) {}
 
  protected:
   virtual ~RenderWidgetHostDelegate() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDER_WIDGET_HOST_DELEGATE_H_