Added support for enabling GCD, or not, at build time.

remoting/webapp/crd/js/plugin_settings.js

 // Copyright (c) 2012 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.
 
 // Contains all the settings that may need massaging by the build script.
 // Keeping all that centralized here allows us to use symlinks for the other
 // files making for a faster compile/run cycle when only modifying HTML/JS.
 
 'use strict';
 
@@ skipping 58 matching lines @@
 remoting.Settings.prototype.XMPP_SERVER_USE_TLS =
     Boolean('XMPP_SERVER_USE_TLS');
 
 // Third party authentication settings.
 /** @type {string} The third party auth redirect URI. */
 remoting.Settings.prototype.THIRD_PARTY_AUTH_REDIRECT_URI =
     'THIRD_PARTY_AUTH_REDIRECT_URL';
 
 // 'native', 'nacl' or 'pnacl'.
 remoting.Settings.prototype.CLIENT_PLUGIN_TYPE = 'CLIENT_PLUGIN_TYPE';
+
+/** @const {boolean} If true, use GCD instead of Chromoting registry. */
+remoting.Settings.prototype.USE_GCD = !!'USE_GCD';