Store AppItems as pages in AppListModel.

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 APP_LIST_EXPORT AppListModelObserver {
  public:
   // Invoked when AppListModel's status has changed.
   virtual void OnAppListModelStatusChanged() {}
 
   // Invoked when AppListModel's profile menu items have changed.
   virtual void OnAppListModelUsersChanged() {}
 
   // Invoked when AppListModel's current user's signin status has changed.
   virtual void OnAppListModelSigninStatusChanged() {}
 
+  // Invoked when items on |page_index| change.
+  virtual void OnListItemsAdded(size_t page_index,

[xiyuan, 2013/10/18 23:04:08]

nit: Rename to OnPageItemsAdded? OnListItemxxxx is bit confusing.

[stevenjb, 2013/10/19 01:04:43]

Sounds reasonable.

+                                size_t start, size_t count) {}
+  virtual void OnListItemsRemoved(size_t page_index,
+                                  size_t start, size_t count) {}
+  virtual void OnListItemMoved(size_t page_index,
+                               size_t index, size_t target_index) {}
+
  protected:
   virtual ~AppListModelObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_MODEL_OBSERVER_H_