Turn on git diff copy detection for git-cl upload.

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 import json
@@ skipping 1110 matching lines @@
     if not options.reviewers and hook_results.reviewers:
       options.reviewers = hook_results.reviewers
 
   # --no-ext-diff is broken in some versions of Git, so try to work around
   # this by overriding the environment (but there is still a problem if the
   # git config key "diff.external" is used).
   env = os.environ.copy()
   if 'GIT_EXTERNAL_DIFF' in env:
     del env['GIT_EXTERNAL_DIFF']
   subprocess2.call(
-      ['git', 'diff', '--no-ext-diff', '--stat', '-M'] + args, env=env)
+      ['git', 'diff', '--no-ext-diff', '--stat', '--find-copies-harder'] + args,
+      env=env)
 
   if settings.GetIsGerrit():
     return GerritUpload(options, args, cl)
   return RietveldUpload(options, args, cl)
 
 
 def SendUpstream(parser, args, cmd):
   """Common code for CmdPush and CmdDCommit
 
   Squashed commit into a single.
@@ skipping 425 matching lines @@
              'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
   # Not a known command. Default to help.
   GenUsage(parser, 'help')
   return CMDhelp(parser, argv)
 
 
 if __name__ == '__main__':
   fix_encoding.fix_encoding()
   sys.exit(main(sys.argv[1:]))