Protect AppListItemList Add/Remove and fix sync bugs

ui/app_list/app_list_item_list_observer.h

 // Copyright (c) 2013 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_ITEM_LIST_OBSERVER_H_
 #define UI_APP_LIST_APP_LIST_ITEM_LIST_OBSERVER_H_
 
 #include "base/basictypes.h"
+#include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class AppListItem;
 
 class APP_LIST_EXPORT AppListItemListObserver {
  public:
   // Triggered after |item| has been added to the list at |index|.
   virtual void OnListItemAdded(size_t index, AppListItem* item) {}
 
   // Triggered after an item has been removed from the list at |index|, just
   // before the item is deleted.
   virtual void OnListItemRemoved(size_t index, AppListItem* item) {}
 
   // Triggered after |item| has been moved from |from_index| to |to_index|.
   virtual void OnListItemMoved(size_t from_index,
                                size_t to_index,
                                AppListItem* item) {}
 
  protected:
   virtual ~AppListItemListObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_ITEM_LIST_OBSERVER_H_