recipe_autoroller: use git cache

recipes/recipe_modules/recipe_autoroller/api.py

 # Copyright 2016 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 hashlib
 import json
 import re
 
 from recipe_engine import recipe_api
 
@@ skipping 145 matching lines @@
       # New commit in A repo will need to get rolled into B first. However,
       # it'd also appear as a candidate for C roll, leading to a failure there.
       if ROLL_FAILURE in results and ROLL_SUCCESS not in results:
         self.m.python.failing_step(
             'roll result',
             'manual intervention needed: automated roll attempt failed')
 
   def _roll_project(self, project_data, recipes_dir):
     with self.m.tempfile.temp_dir('roll_%s' % project_data['id']) as workdir:
       self.m.git.checkout(
-          project_data['repo_url'], dir_path=workdir, submodules=False)
+          project_data['repo_url'], dir_path=workdir, submodules=False,
+          use_git_cache=True)
 
       # Introduce ourselves to git - also needed for git cl upload to work.
       self.m.git(
           'config', 'user.email', 'recipe-roller@chromium.org', cwd=workdir)
       self.m.git('config', 'user.name', 'recipe-roller', cwd=workdir)
 
       # git cl upload cannot work with detached HEAD, it requires a branch.
       self.m.git('checkout', '-t', '-b', 'roll', 'origin/master', cwd=workdir)
 
       recipes_cfg_path = workdir.join('infra', 'config', 'recipes.cfg')
@@ skipping 103 matching lines @@
         'issue': m.group(1),
         'issue_url': m.group(2),
         'diff_digest': diff_digest,
       }
       issue_result.presentation.links['Issue %s' % change_data['issue']] = (
           change_data['issue_url'])
       self.m.gsutil.upload(
           self.m.json.input(change_data),
           'recipe-roller-cl-uploads',
           cfg_digest)