Add Popen.start property.

tests/subprocess2_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.
 
 """Unit tests for subprocess2.py."""
 
 import logging
 import optparse
 import os
@@ skipping 124 matching lines @@
     if sys.platform != 'win32':
       env = os.environ.copy()
       is_english = lambda name: env.get(name, 'en').startswith('en')
       if not is_english('LANG'):
         env['LANG'] = 'en_US.UTF-8'
         expected['env'] = env
       if not is_english('LANGUAGE'):
         env['LANGUAGE'] = 'en_US.UTF-8'
         expected['env'] = env
     self.assertEquals(expected, results)
+    self.assertTrue(time.time() >= proc.start)
 
   def test_check_output_defaults(self):
     results = self._fake_communicate()
     # It's discarding 'stderr' because it assumes stderr=subprocess2.STDOUT but
     # fake_communicate() doesn't 'implement' that.
     self.assertEquals('stdout', subprocess2.check_output(['foo'], a=True))
     expected = {
         'args': ['foo'],
         'a':True,
         'stdin': subprocess2.VOID,
@@ skipping 223 matching lines @@
   return options.return_value
 
 
 if __name__ == '__main__':
   logging.basicConfig(level=
       [logging.WARNING, logging.INFO, logging.DEBUG][
         min(2, sys.argv.count('-v'))])
   if len(sys.argv) > 1 and sys.argv[1] == '--child':
     sys.exit(child_main(sys.argv[2:]))
   unittest.main()