Migrate dartium_tools from chrome branch to dart repo

tools/dartium/set_reference_build_revision.py

 #!/usr/bin/env python
 #
 # Copyright (c) 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.
 
 """Writes a revision number into src/chrome/tools/test/reference_build/REVISON
    Must be run from the root of a Dartium or multivm checkout.
 
 Usage:
-  $ ./src/dart/tools/bots/set_reference_build_revision.py <revision>
+  $ ./src/dart/tools/dartium/set_reference_build_revision.py <revision>
 """
 
 import os
 import sys
 
 def main(argv):
   revision = argv[1]
   output = os.path.join('src', 'chrome', 'tools',
                         'test', 'reference_build',
                         'REQUESTED_REVISION')
   dirname = os.path.dirname(output)
   if dirname and not os.path.exists(dirname):
     os.makedirs(dirname)
   with file(output, 'w') as f:
     f.write(revision)
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))