Add ChromiumOS Trybot support.

test/masters_test.py

 #!/usr/bin/env python
 # Copyright (c) 2011 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.
 
 """Starts all masters and verify they can server /json/project fine.
 """
 
 from __future__ import with_statement
 import logging
@@ skipping 206 matching lines @@
       'master.client.sfntly': None,
       'master.client.skia': None,
       'master.client.syzygy': None,
       'master.client.tsan': None,  # make start fails
       'master.client.v8': 'V8',
       'master.client.webm': 'WebM',
       'master.experimental': None,
       'master.reserved': None,  # make start fails
       'master.tryserver.chromium': 'Chromium Try Server',
       'master.tryserver.nacl': 'NativeClient-Try',
+      'master.tryserver.chromiumos': 'ChromiumOS Try Server',
   }
   return real_main(base_dir, expected)
 
 
 if __name__ == '__main__':
   sys.exit(main())