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

ash/common/system/tray/tray_image_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_TRAY_IMAGE_ITEM_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_IMAGE_ITEM_H_
 
 #include "ash/ash_export.h"
 #include "ash/common/system/tray/system_tray_item.h"
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 
 namespace views {
 class ImageView;
 }
 
 namespace ash {
 class TrayItemView;
 
+// A system tray item that uses an image as its "tray view" in the status area.
 class ASH_EXPORT TrayImageItem : public SystemTrayItem {
  public:
   TrayImageItem(SystemTray* system_tray, int resource_id, UmaType uma_type);
   ~TrayImageItem() override;
 
   views::View* tray_view();
 
  protected:
   virtual bool GetInitialVisibility() = 0;
 
@@ skipping 20 matching lines @@
   void UpdateImageOnImageView();
 
   // The resource ID for the non-material design icon in the tray.
   // TODO(tdanderson): This is only used for non-material design, so remove it
   // when material design is the default. See crbug.com/625692.
   int resource_id_;
 
   // The color of the material design icon in the tray.
   SkColor icon_color_;
 
+  // The image view in the tray.
   TrayItemView* tray_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayImageItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_IMAGE_ITEM_H_