git cl upload now diffs HEAD rather than working tree

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 1254 matching lines @@
   if is_dirty_git_tree('upload'):
     return 1
 
   cl = Changelist()
   if args:
     # TODO(ukai): is it ok for gerrit case?
     base_branch = args[0]
   else:
     # Default to diffing against common ancestor of upstream branch
     base_branch = RunGit(['merge-base', cl.GetUpstreamBranch(), 'HEAD']).strip()
-    args = [base_branch]
+    args = [base_branch, 'HEAD']
 
   if not options.bypass_hooks:
     hook_results = cl.RunHook(committing=False, upstream_branch=base_branch,
                               may_prompt=not options.force,
                               verbose=options.verbose,
                               author=None)
     if not hook_results.should_continue():
       return 1
     if not options.reviewers and hook_results.reviewers:
       options.reviewers = hook_results.reviewers
@@ skipping 597 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:]))