Enable --git-cache-dir option in chromite/cbuildbot.

scripts/slave/recipe_modules/chromite/api.py

 # Copyright 2013 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.
 
 import cgi
 import re
 
 from recipe_engine import recipe_api
 
 
@@ skipping 400 matching lines @@
     if self.c.cbb.debug:
       cbb_args.extend(['--debug'])
     if self.c.cbb.clobber:
       cbb_args.extend(['--clobber'])
     if self.c.cbb.chrome_version:
       cbb_args.extend(['--chrome_version', self.c.cbb.chrome_version])
     if self.c.cbb.config_repo:
       cbb_args.extend(['--config_repo', self.c.cbb.config_repo])
     if self.c.cbb.buildbucket_id:
       cbb_args.extend(['--buildbucket-id', self.c.cbb.buildbucket_id])
-    if self.c.repo_cache_dir and self.c.cbb.supports_repo_cache:
+
+    # These flags are mutually exclusive.
+    # TODO(nxia): Remove "repo_cache" support after "git_cache" has rolled out.
+    if self.c.cbb.git_cache_dir:
+      cbb_args.extend(['--git-cache-dir', self.c.cbb.git_cache_dir])
+    elif self.c.repo_cache_dir and self.c.cbb.supports_repo_cache:
       cbb_args.extend(['--repo-cache', self.c.repo_cache_dir])
 
     # Set the build ID, if specified.
     if self.c.cbb.build_id:
       cbb_args.extend(['--master-build-id', self.c.cbb.build_id])
 
     # Add custom args, if there are any.
     cbb_args.extend(args)
 
     # Run cbuildbot.
     return self.cbuildbot(str('cbuildbot [%s]' % (self.c.cbb.config,)),
                           self.c.cbb.config,
                           args=cbb_args,
                           cwd=self.m.path['slave_build'])