Create a new depot_tools_testing_lib to move utility modules there

tests/owners_unittest.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.
 
 """Unit tests for owners.py."""
 
 import os
 import sys
 import unittest
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+from testing_support import filesystem_mock
+
 import owners
-from tests import filesystem_mock
 
 ben = 'ben@example.com'
 brett = 'brett@example.com'
 darin = 'darin@example.com'
 john = 'john@example.com'
 ken = 'ken@example.com'
 peter = 'peter@example.com'
 
 def owners_file(*email_addresses, **kwargs):
   s = ''
@@ skipping 144 matching lines @@
 
   def test_syntax_error__unknown_set(self):
     self.assert_syntax_error('set myfatherisbillgates\n')
 
   def test_syntax_error__bad_email(self):
     self.assert_syntax_error('ben\n')
 
 
 if __name__ == '__main__':
   unittest.main()