ash: Use system tray mojo interface to show system update tray icon

ash/common/system/tray/system_tray_item.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 ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_
 #define ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
 #include "ash/common/login_status.h"
 #include "ash/public/cpp/shelf_types.h"
 #include "base/macros.h"
 
 namespace base {
 class OneShotTimer;
 }  // namespace base
 
 namespace views {
 class View;
 }
 
 namespace ash {
 class SystemTray;
 class SystemTrayBubble;
 class TrayItemView;
 
+// Controller for an item in the system tray. Each item can create these views:
+// Tray view - The icon in the status area in the shelf.
+// Default view - The row in the top-level menu.
+// Detailed view - The submenu shown when the top-level menu row is clicked.
 class ASH_EXPORT SystemTrayItem {
  public:
   // The different types of SystemTrayItems.
   //
   // NOTE: These values are used for UMA metrics so do NOT re-order this enum
   // and only insert items before the COUNT item.
   enum UmaType {
     // SystemTrayItem's with this type are not recorded in the histogram.
     UMA_NOT_RECORDED = 0,
     // Used for testing purposes only.
@@ skipping 42 matching lines @@
   // Returns a view for the item to be displayed in the list. This view can be
   // displayed with a number of other tray items, so this should not be too
   // big.
   virtual views::View* CreateDefaultView(LoginStatus status);
 
   // Returns a detailed view for the item. This view is displayed standalone.
   virtual views::View* CreateDetailedView(LoginStatus status);
 
   // Returns a notification view for the item. This view is displayed with
   // other notifications and should be the same size as default views.
+  // DEPRECATED. Use the message center instead.
   virtual views::View* CreateNotificationView(LoginStatus status);
 
   // These functions are called when the corresponding view item is about to be
   // removed. An item should do appropriate cleanup in these functions.
   // The default implementation does nothing.
   virtual void DestroyTrayView();
   virtual void DestroyDefaultView();
   virtual void DestroyDetailedView();
   virtual void DestroyNotificationView();
 
@@ skipping 63 matching lines @@
 
   // Used to delay the transition to the detailed view.
   std::unique_ptr<base::OneShotTimer> transition_delay_timer_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTrayItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_SYSTEM_TRAY_ITEM_H_