mash: Cleanup ash shelf application menu code.

ash/public/cpp/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.
 
 # C++ headers and sources that can be used outside ash.
 component("ash_public_cpp") {
   sources = [
     "ash_public_export.h",
     "mus_property_mirror_ash.cc",
     "mus_property_mirror_ash.h",
     "session_types.h",
+    "shelf_application_menu_item.cc",
+    "shelf_application_menu_item.h",
     "shelf_types.h",
     "shell_window_ids.cc",
     "shell_window_ids.h",
     "window_properties.cc",
     "window_properties.h",
   ]
 
   defines = [ "ASH_PUBLIC_IMPLEMENTATION" ]
 
   deps = [
     "//base",
     "//ui/aura",
     "//ui/views/mus",
   ]
 }