Shutdown multiprocess pool after running tests to avoid _finalizer spew on Windows

tests/presubmit_unittest.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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 presubmit_support.py and presubmit_canned_checks.py."""
 
 # pylint: disable=E1101,E1103
 
 import StringIO
@@ skipping 1235 matching lines @@
         'DepotToLocalPath',
         'FilterSourceFile',
         'LocalPaths',
         'LocalToDepotPath',
         'Command',
         'RunTests',
         'PresubmitLocalPath',
         'ReadFile',
         'RightHandSideLines',
         'ServerPaths',
+        'ShutdownPool',
         'basename',
         'cPickle',
         'cpplint',
         'cStringIO',
         'canned_checks',
         'change',
         'cpu_count',
         'environ',
         'fnmatch',
         'glob',
@@ skipping 1831 matching lines @@
         owners_check=False)
     self.assertEqual(2, len(results))
     self.assertEqual(
         'Found line ending with white spaces in:', results[0]._message)
     self.checkstdout('')
 
 
 if __name__ == '__main__':
   import unittest
   unittest.main()