Make export_tarball.py work with older Pythons.

tools/export_tarball/export_tarball.py

 #!/usr/bin/python
 # Copyright (c) 2009 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.
 
 """
 This tool creates a tarball with all the sources, but without .svn directories.
 
 It can also remove files which are not strictly required for build, so that
 the resulting tarball can be reasonably small (last time it was ~110 MB).
 
 Example usage:
 
 export_tarball.py /foo/bar
 
 The above will create file /foo/bar.tar.bz2.
 """
 
-from __future__ import with_statement
-
-import contextlib
 import optparse
 import os
 import sys
 import tarfile
 
 NONESSENTIAL_DIRS = (
     'chrome/test/data',
     'chrome/tools/test/reference_build',
     'gears/binaries',
     'net/data/cache_tests',
@@ skipping 35 matching lines @@
       return True
 
     if not options.remove_nonessential_files:
       return False
     for nonessential_dir in NONESSENTIAL_DIRS:
       if path.startswith(os.path.join(GetSourceDirectory(), nonessential_dir)):
         return True
 
     return False
 
-  with contextlib.closing(tarfile.open(output_fullname, 'w:bz2')) as archive:
+  archive = tarfile.open(output_fullname, 'w:bz2')
+  try:
     archive.add(GetSourceDirectory(), arcname=output_basename,
                 exclude=ShouldExcludePath)
+  finally:
+    archive.close()
 
   return 0
 
 if __name__ == "__main__":
   sys.exit(main(sys.argv[1:]))