Refactor cache-updating code to eliminate unnecessary fetches.

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 300 matching lines @@
           'Extracting bootstrap zipfile %s failed.\n'
           'Resuming normal operations.' % filename)
       return False
     return True
 
   def exists(self):
     return os.path.isfile(os.path.join(self.mirror_path, 'config'))
 
   def populate(self, depth=None, shallow=False, bootstrap=False,
                verbose=False):
+    assert self.GetCachePath()
     if shallow and not depth:
       depth = 10000
     gclient_utils.safe_makedirs(self.GetCachePath())
 
     v = []
     if verbose:
       v = ['-v', '--progress']
 
     d = []
     if depth:
@@ skipping 90 matching lines @@
       os.remove(lf)
       did_unlock = True
     return did_unlock
 
   def unlock(self):
     return self.BreakLocks(self.mirror_path)
 
   @classmethod
   def UnlockAll(cls):
     cachepath = cls.GetCachePath()
+    if not cachepath:
+      return
     dirlist = os.listdir(cachepath)
     repo_dirs = set([os.path.join(cachepath, path) for path in dirlist
                      if os.path.isdir(os.path.join(cachepath, path))])
     for dirent in dirlist:
       if (dirent.endswith('.lock') and
           os.path.isfile(os.path.join(cachepath, dirent))):
         repo_dirs.add(os.path.join(cachepath, dirent[:-5]))
 
     unlocked_repos = []
     for repo_dir in repo_dirs:
@@ skipping 132 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:]))