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

remoting/remoting_options.gypi

 # 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.
 
 {
   'variables': {
     'chromium_code': 1,
 
     # Set this to run the jscompile checks after building the webapp.
     'run_jscompile%': 1,
 
     # Set this to enable cast mode on the android client.
     'enable_cast%': 0,
+ 
+    # Set this to use GCD instead of the remoting directory service.
+    'remoting_use_gcd%': 0,
 
     'variables': {
       'conditions': [
         # Enable the multi-process host on Windows by default.
         ['OS=="win"', {
           'remoting_multi_process%': 1,
         }, {
           'remoting_multi_process%': 0,
         }],
       ],
     },
     'remoting_multi_process%': '<(remoting_multi_process)',
 
     'remoting_rdp_session%': 1,
 
     'branding_path': '../remoting/branding_<(branding)',
 
     'conditions': [
       ['OS=="win"', {
         # Java is not available on Windows bots, so we need to disable
         # JScompile checks.
         'run_jscompile': 0,
       }],
     ],
   },
 
 }