Don't os.listdir() on a non-existent dir (it raises).

git_cache.py

 #!/usr/bin/env python
 # Copyright 2014 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.
 
 """A git command for managing a local cache of git repositories."""
 
 from __future__ import print_function
 import errno
 import logging
@@ skipping 381 matching lines @@
     subprocess.call(['zip', '-r', tmp_zipfile, '.'], cwd=self.mirror_path)
     gsutil = Gsutil(path=self.gsutil_exe, boto_path=None)
     dest_name = 'gs://%s/%s/%s.zip' % (
         self.bootstrap_bucket, self.basedir, gen_number)
     gsutil.call('cp', tmp_zipfile, dest_name)
     os.remove(tmp_zipfile)
 
   @staticmethod
   def DeleteTmpPackFiles(path):
     pack_dir = os.path.join(path, 'objects', 'pack')
+    if not os.path.isdir(pack_dir):
+      return
     pack_files = [f for f in os.listdir(pack_dir) if
                   f.startswith('.tmp-') or f.startswith('tmp_pack_')]
     for f in pack_files:
       f = os.path.join(pack_dir, f)
       try:
         os.remove(f)
         logging.warn('Deleted stale temporary pack file %s' % f)
       except OSError:
         logging.warn('Unable to delete temporary pack file %s' % f)
 
@@ skipping 167 matching lines @@
     return options, args
 
 
 def main(argv):
   dispatcher = subcommand.CommandDispatcher(__name__)
   return dispatcher.execute(OptionParser(), argv)
 
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv[1:]))