Set returncode to subprocess2.TIMED_OUT instead of -9 when a process times out.

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 optparse
 import os
 import sys
@@ skipping 118 matching lines @@
         'stderr': subprocess2.STDOUT,
     }
     self.assertEquals(expected, results)
 
   def test_timeout(self):
     # It'd be better to not discard stdout.
     out, returncode = subprocess2.call(
         self.exe + ['--sleep', '--stdout'],
         timeout=0.01,
         stdout=subprocess2.PIPE)
-    self.assertEquals(-9, returncode)
+    self.assertEquals(subprocess2.TIMED_OUT, returncode)
     self.assertEquals(['', None], out)
 
   def test_void(self):
     out = subprocess2.check_output(
          self.exe + ['--stdout', '--stderr'],
          stdout=subprocess2.VOID)
     self.assertEquals(None, out)
     out = subprocess2.check_output(
          self.exe + ['--stdout', '--stderr'],
           universal_newlines=True,
@@ skipping 46 matching lines @@
   do('CCC')
   if options.sleep:
     time.sleep(10)
   return options.return_value
 
 
 if __name__ == '__main__':
   if len(sys.argv) > 1 and sys.argv[1] == '--child':
     sys.exit(child_main(sys.argv[2:]))
   unittest.main()