Protect AppListItemList Add/Remove and fix sync bugs

ui/app_list/app_list_model_observer.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 UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_
 #define UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_
 
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
+class AppListItem;
+
 class APP_LIST_EXPORT AppListModelObserver {
  public:
   // Invoked when AppListModel's status has changed.
   virtual void OnAppListModelStatusChanged() {}
 
+  // Triggered after |item| has been added to the model.
+  virtual void OnAppListItemAdded(AppListItem* item) {}
+
+  // Triggered just before an item is deleted from the model.
+  virtual void OnAppListItemWillBeDeleted(AppListItem* item) {}
+
+  // Triggered after |item| has moved or changed folders.
+  virtual void OnAppListItemUpdated(AppListItem* item) {}
+
  protected:
   virtual ~AppListModelObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_