[AppRemoting] Break out AppRemoting shared module (re-land).

remoting/webapp/base/js/app_capabilities.js

-// 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.
-
-'use strict';
-
-/** @suppress {duplicate} */
-var remoting = remoting || {};
-
-/**
- * Note that this needs to be a function because it gets expanded at
- * compile-time into remoting.ClientSession.Capability enums and these
- * are not guaranteed to be present yet when this file is loaded.
- * @return {Array<remoting.ClientSession.Capability>}
- */
-remoting.app_capabilities = function() {
-  return ['APPLICATION_CAPABILITIES'];
-}