mash: Port TrayUpdateTest to AshTest

ash/common/BUILD.gn

 # Copyright 2016 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.
 
 source_set("unittests") {
   testonly = true
   sources = [
     "accelerators/accelerator_table_unittest.cc",
+    "system/update/tray_update_unittest.cc",
     "wm/container_finder_unittest.cc",
     "wm/workspace/workspace_layout_manager_unittest.cc",
     "wm_window_unittest.cc",
     "wm_window_user_data_unittest.cc",
   ]
   deps = [
     "//ash",
     "//ash/common/test:test_support",
     "//ash/test:test_support_without_content",
     "//ui/base",
     "//ui/display",
     "//ui/keyboard",
     "//ui/views",
     "//ui/wm",
   ]
 
   if (is_chromeos) {
     sources += [ "system/chromeos/brightness/tray_brightness_unittest.cc" ]
   }
 }