[Chromoting] Add ability to enable/disable GDrive support per-app in gyp.

remoting/webapp/app_remoting/manifest_common.json.jinja2

   {{ MANIFEST_KEY_FOR_UNOFFICIAL_BUILD }}
   "name": "{{APP_NAME}}",
   "description": "{{APP_DESCRIPTION}}",
   "version": "{{ FULL_APP_VERSION }}",
   "manifest_version": 2,
   "default_locale": "en",
   "app": {
     "background": {
       "scripts": ["ar_background.js", "platform.js"]
     }
@@ skipping 31 matching lines @@
         "udp-bind",
         "udp-multicast-membership",
         "resolve-host",
         "network-state"
       ]
     }
   ],
   "oauth2": {
     "client_id": "{{ REMOTING_IDENTITY_API_CLIENT_ID }}",
     "scopes": [
-      "https://www.googleapis.com/auth/appremoting.runapplication https://www.googleapis.com/auth/googletalk https://www.googleapis.com/auth/userinfo#email https://www.googleapis.com/auth/userinfo.profile https://docs.google.com/feeds/ https://www.googleapis.com/auth/drive"
+      "https://www.googleapis.com/auth/appremoting.runapplication https://www.googleapis.com/auth/googletalk https://www.googleapis.com/auth/userinfo#email https://www.googleapis.com/auth/userinfo.profile {{ OAUTH_GDRIVE_SCOPE }}"
     ]
   },
   "sandbox": {
     "pages": [ "wcs_sandbox.html" ]
   }