mus: Fix handled status in UI event ack, add MessageLoop::NestingObserver

ui/views/mus/BUILD.gn

 # Copyright 2014 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("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//mojo/public/mojo_application.gni")
 import("//testing/test.gni")
 import("//tools/grit/repack.gni")
 
@@ skipping 132 matching lines @@
   # TODO(sky): add more files.
   sources = [
     "../run_all_unittests.cc",
     "../run_all_unittests.h",
     "../test/native_widget_factory_mus.cc",
     "../view_targeter_unittest.cc",
     "../widget/native_widget_unittest.cc",
     "../widget/widget_unittest.cc",
     "native_widget_mus_unittest.cc",
     "platform_test_helper_mus.cc",
+    "platform_window_mus_unittest.cc",
     "run_all_unittests_mus.cc",
     "screen_mus_unittest.cc",
   ]
 
   deps = [
     ":mus",
     "//base",
     "//base:i18n",
     "//base/test:test_support",
     "//cc",
@@ skipping 68 matching lines @@
 }
 
 group("for_component") {
   public_deps = [
     ":mus",
   ]
   deps = [
     "//mojo/gles2",
   ]
 }