Make git_cache.py import-able.

gclient.py

Index: gclient.py
diff --git a/gclient.py b/gclient.py
index 5fa356540598336da96504eaf4c36e5c995466c4..5c5c5ca5f57f4ae3cb692e8fa2c7f51167fedd43 100755
--- a/gclient.py
+++ b/gclient.py
@@ -97,6 +97,7 @@ import breakpad  # pylint: disable=W0611
 import fix_encoding
 import gclient_scm
 import gclient_utils
+import git_cache
 from third_party.repo.progress import Progress
 import subcommand
 import subprocess2
@@ -1094,6 +1095,7 @@ want to set 'managed': False in .gclient.
       self._enforced_os = tuple(set(self._enforced_os).union(target_os))
 
     gclient_scm.GitWrapper.cache_dir = config_dict.get('cache_dir')
+    git_cache.Mirror.SetCachePath(config_dict.get('cache_dir'))
 
     if not target_os and config_dict.get('target_os_only', False):
       raise gclient_utils.Error('Can\'t use target_os_only if target_os is '