Protect AppListItemList Add/Remove and fix sync bugs

ui/app_list/app_list_folder_item.h

 // Copyright 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_FOLDER_ITEM_H_
 #define UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 25 matching lines @@
 
   AppListItemList* item_list() { return item_list_.get(); }
 
   static const char kItemType[];
 
   // Calculates the top item icons' bounds inside |folder_icon_bounds|.
   // Returns the bounds of top item icons in sequence of top left, top right,
   // bottom left, bottom right.
   static Rects GetTopIconsBounds(const gfx::Rect& folder_icon_bounds);
 
+  // Returns an id for a new folder.
+  static std::string GenerateId();
+
  private:
   // AppListItem
   virtual void Activate(int event_flags) OVERRIDE;
   virtual const char* GetItemType() const OVERRIDE;
   virtual ui::MenuModel* GetContextMenuModel() OVERRIDE;
 
   // AppListItemObserver
   virtual void ItemIconChanged() OVERRIDE;
   virtual void ItemTitleChanged() OVERRIDE;
   virtual void ItemHighlightedChanged() OVERRIDE;
@@ skipping 13 matching lines @@
   scoped_ptr<AppListItemList> item_list_;
   // Top items for generating folder icon.
   std::vector<AppListItem*> top_items_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListFolderItem);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_FOLDER_ITEM_H_