Reland of Add rudimentary shelf delegate mus unit test.

mash/BUILD.gn

 # Copyright 2015 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.
 
 import("//mojo/public/mojo_application_manifest.gni")
 import("//testing/test.gni")
 
 # Target that builders build.
 group("all") {
   testonly = true
 
   deps = [
     ":mash_unittests",
     "//components/leveldb",
     "//mash/catalog_viewer",
     "//mash/example",
     "//mash/init",
     "//mash/login",
     "//mash/screenlock",
     "//mash/session",
     "//mash/task_viewer",
   ]
 }
 
 test("mash_unittests") {
   deps = [
+    "//ash/mus:unittests",
     "//base",
     "//base/test:test_config",
     "//base/test:test_support",
     "//mash/wm:unittests",
     "//mojo/platform_handle:platform_handle_impl",
     "//services/shell/background:main",
     "//services/shell/public/cpp/test:run_all_shelltests",
   ]
   data_deps = [
     ":unittests_manifest",
   ]
 }
 
 mojo_application_manifest("unittests_manifest") {
   type = "exe"
   application_name = "mash_unittests"
   source = "unittests_manifest.json"
 }