Protect AppListItemList Add/Remove and fix sync bugs

ui/app_list/app_list_folder_item.cc

 // 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.
 
 #include "ui/app_list/app_list_folder_item.h"
 
+#include "base/guid.h"
 #include "ui/app_list/app_list_constants.h"
 #include "ui/app_list/app_list_item_list.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/image/canvas_image_source.h"
 #include "ui/gfx/image/image_skia_operations.h"
 
 namespace app_list {
 
 namespace {
 
@@ skipping 120 matching lines @@
   top_icon_bounds.push_back(bottom_left);
 
   // Get the bottom right icon bounds.
   gfx::Rect bottom_right(
       right_x, bottom_y, kItemIconDimension, kItemIconDimension);
   top_icon_bounds.push_back(bottom_right);
 
   return top_icon_bounds;
 }
 
+std::string AppListFolderItem::GenerateId() {
+  return base::GenerateGUID();
+}
+
 const char* AppListFolderItem::GetItemType() const {
   return AppListFolderItem::kItemType;
 }
 
 ui::MenuModel* AppListFolderItem::GetContextMenuModel() {
   // TODO(stevenjb/jennyz): Implement.
   return NULL;
 }
 
 void AppListFolderItem::ItemIconChanged() {
@@ skipping 39 matching lines @@
   for (size_t i = 0;
        i < kNumFolderTopItems && i < item_list_->item_count(); ++i) {
     AppListItem* item = item_list_->item_at(i);
     item->AddObserver(this);
     top_items_.push_back(item);
   }
   UpdateIcon();
 }
 
 }  // namespace app_list