[win] Add a progress bar in the app launcher for app installs.

ui/app_list/app_list_item_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_ITEM_MODEL_OBSERVER_H_
 #define UI_APP_LIST_APP_LIST_ITEM_MODEL_OBSERVER_H_
 
 #include "ui/app_list/app_list_export.h"
 
 namespace app_list {
 
 class APP_LIST_EXPORT AppListItemModelObserver {
  public:
   // Invoked after item's icon is changed.
   virtual void ItemIconChanged() = 0;
 
   // Invoked after item's title is changed.
   virtual void ItemTitleChanged() = 0;
 
   // Invoked after item's highlighted state is changed.
   virtual void ItemHighlightedChanged() = 0;
 
+  // Invoked after item begins or finishes installing.
+  virtual void ItemIsInstallingChanged() = 0;
+
+  // Invoked after item's download percentage changes.
+  virtual void ItemPercentDownloadedChanged() = 0;
+
  protected:
   virtual ~AppListItemModelObserver() {}
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_APP_LIST_ITEM_MODEL_OBSERVER_H_