Avoid unnecessary file churn by "git reset --hard" step.

scripts/slave/gclient_safe_revert.py

 #!/usr/bin/env python
 # Copyright (c) 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.
 
 """Do a revert if a checkout exists."""
 
 import os
 import sys
 
@@ skipping 25 matching lines @@
   if not os.path.exists(gclient_config):
     print ('%s doesn\'t exist, not a gclient-controlled checkout.' %
               gclient_config)
     return 0
 
   # Work around http://crbug.com/280158
   cmd = [gclient_command, 'recurse', '-i', 'sh', '-c',
          'if [ -e .git ]; then git remote update; fi']
   chromium_utils.RunCommand(cmd, cwd=build_directory)
 
+  # Work around http://crbug.com/642711
+  cmd = [gclient_command, 'recurse', '-v', 'git', 'update-index', '--refresh']
+  chromium_utils.RunCommand(cmd, cwd=build_directory)
+
   cmd = [gclient_command, 'revert', '-v', '-v', '-v', '--nohooks', '--upstream']
   return chromium_utils.RunCommand(cmd, cwd=build_directory)
 
 
 if '__main__' == __name__:
   sys.exit(main())