Reland: mash: Fix MusPropertyMirrorAsh for owned properties; add test.

ash/common/test/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.
 
 static_library("test_support") {
   testonly = true
   sources = [
     "ash_test.cc",
     "ash_test.h",
     "ash_test_impl.h",
@@ skipping 14 matching lines @@
     "workspace_event_handler_test_helper.cc",
     "workspace_event_handler_test_helper.h",
   ]
   configs += [ "//build/config:precompiled_headers" ]
 
   public_deps = [
     "//testing/gtest",
   ]
   deps = [
     "//ash",
-    "//ash/public/cpp",
+    "//ash/public/cpp:ash_public_cpp",
     "//ash/public/interfaces",
     "//base",
     "//components/signin/core/account_id",
     "//components/user_manager",
 
     # TODO: this is for ui/wm/public/window_types.h, which is in aura.
     # http://crbug.com/654078.
     "//ui/aura",
     "//ui/display/manager",
     "//ui/gfx/geometry",
     "//ui/views",
     "//ui/wm",
   ]
 }