backup for dynamic recent tabs submenu

ui/base/models/menu_model_delegate.h

 // Copyright (c) 2010 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 UI_BASE_MODELS_MENU_MODEL_DELEGATE_H_
 #define UI_BASE_MODELS_MENU_MODEL_DELEGATE_H_
 
 namespace ui {
 
 class MenuModelDelegate {
  public:
   // Invoked when an icon has been loaded from history.
   virtual void OnIconChanged(int index) = 0;
 
+  // Invoked prior to any calls to OnItemAdded()/OnItemRemoved().
+  virtual void PrepareForChange() {}
+
+  // Invoked when adding and removing items in MenuModel, delegate should
+  // add or remove items to or from the menu as per the model.
+  virtual void OnItemAdded(int index) {}
+  virtual void OnItemRemoved(int index) {}
+
+  // Invoked when MenuModel has finisheed the changes, delegate should finalize
+  // the menu and update the UI.
+  virtual void ChangesDone() {}
+
  protected:
   virtual ~MenuModelDelegate() {}
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_MODELS_MENU_MODEL_DELEGATE_H_