Add owners file to GN bootstrap.

tools/gn/bootstrap/bootstrap.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
+# This file isn't officially supported by the Chromium project. It's maintained
+# on a best-effort basis by volunteers, so some things may be broken from time
+# to time. If you encounter errors, it's most often due to files in base that
+# have been added or moved since somebody last tried this script. Generally
+# such errors are easy to diagnose.
+
 """Bootstraps gn.
 
 It is done by first building it manually in a temporary directory, then building
 it with its own BUILD.gn to the final destination.
 """
 
 import contextlib
 import errno
 import logging
 import optparse
@@ skipping 435 matching lines @@
     cmd.append('-v')
   cmd.append('gn')
   check_call(cmd)
 
   if not options.debug:
     check_call(['strip', os.path.join(build_dir, 'gn')])
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))