Protect AppListItemList Add/Remove and fix sync bugs

ui/app_list/test/app_list_test_model.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/test/app_list_test_model.h"
 
 #include "base/strings/stringprintf.h"
 
 namespace app_list {
 namespace test {
@@ skipping 66 matching lines @@
     position = syncer::StringOrdinal::CreateInitialOrdinal();
   else
     position = item_list()->item_at(nitems - 1)->position().CreateAfter();
   item->SetPosition(position);
   item->SetTitleAndFullName(title, full_name);
   return item;
 }
 
 void AppListTestModel::CreateAndAddItem(const std::string& title,
                                         const std::string& full_name) {
-  item_list()->AddItem(CreateItem(title, full_name));
+  AddItem(CreateItem(title, full_name));
 }
 
 void AppListTestModel::CreateAndAddItem(const std::string& title) {
   CreateAndAddItem(title, title);
 }
 
 void AppListTestModel::HighlightItemAt(int index) {
   AppListItem* item = item_list()->item_at(index);
   item->SetHighlighted(true);
 }
 
 void AppListTestModel::ItemActivated(AppListTestItemModel* item) {
   last_activated_ = item;
   ++activate_count_;
 }
 
 }  // namespace test
 }  // namespace app_list