mash: Fix MusPropertyMirrorAsh for owned properties; add test.

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.
 
 assert(is_chromeos)
 
 source_set("unittests") {
   testonly = true
   sources = [
     "accelerators/accelerator_table_unittest.cc",
     "drag_drop/drag_image_view_unittest.cc",
+    "mus_property_mirror_ash_unittest.cc",
     "system/chromeos/audio/tray_audio_unittest.cc",
     "system/chromeos/brightness/tray_brightness_unittest.cc",
     "system/chromeos/network/vpn_list_unittest.cc",
     "system/chromeos/screen_security/screen_tray_item_unittest.cc",
     "system/chromeos/supervised/tray_supervised_user_unittest.cc",
     "system/date/date_view_unittest.cc",
     "system/update/tray_update_unittest.cc",
     "wm/container_finder_unittest.cc",
     "wm/mru_window_tracker_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/public/cpp",
     "//ash/public/interfaces",
     "//ash/test:test_support_without_content",
     "//ui/aura",
     "//ui/base",
     "//ui/display",
     "//ui/keyboard",
     "//ui/message_center",
     "//ui/views",
     "//ui/wm",
   ]
 }