ash: Add a unit test for the system update tray item

ash/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_SYSTEM_TRAY_TRAY_IMAGE_ITEM_H_
 #define ASH_SYSTEM_TRAY_TRAY_IMAGE_ITEM_H_
 
+#include "ash/ash_export.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/macros.h"
 
 namespace views {
 class ImageView;
 }
 
 namespace ash {
 class TrayItemView;
 
-class TrayImageItem : public SystemTrayItem {
+class ASH_EXPORT TrayImageItem : public SystemTrayItem {
  public:
   TrayImageItem(SystemTray* system_tray, int resource_id);
   ~TrayImageItem() override;
 
   views::View* tray_view();
 
   // Changes the icon of the tray-view to the specified resource.
   void SetImageFromResourceId(int resource_id);
 
  protected:
@@ skipping 15 matching lines @@
 
   int resource_id_;
   TrayItemView* tray_view_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayImageItem);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_TRAY_IMAGE_ITEM_H_