Make it possible to enable remoting_audio via GYP_DEFINES.

remoting/remoting.gyp

 # 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': {
     # TODO(dmaclach): can we pick this up some other way? Right now it's
     # duplicated from chrome.gyp
     'chromium_code': 1,
 
-    'remoting_audio': 0,
+    'remoting_audio%': 0,
     'remoting_multi_process%': 0,
 
     # Use consistent strings across all platforms. Note that the plugin name
     # is brand-dependent and is defined further down.
     # Must match host/plugin/constants.h
     'host_plugin_mime_type': 'application/vnd.chromium.remoting-host',
     'host_plugin_description': 'Allow another user to access your computer securely over the Internet.',
 
     # The version is composed from major & minor versions specific to remoting
     # and build & patch versions inherited from Chrome.
@@ skipping 1835 matching lines @@
                   '../base/allocator/allocator.gyp:allocator',
                 ],
               },
             ],
           ],
         }],
       ],  # end of 'conditions'
     },  # end of target 'remoting_unittests'
   ],  # end of targets
 }