Update the index in SendUpstream before tree check.

BUG=none
TEST=git cl dcommit/push performs an index update before
checking if the tree is dirty
Review URL: http://codereview.chromium.org/6172003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@70908 0039d316-1c4b-4281-b951-d872f2087c98

git_cl/git_cl.py

@@ -859,6 +859,8 @@ def SendUpstream(parser, args, cmd):
 
   base_branch = args[0]
 
+  # Make sure index is up-to-date before running diff-index.
+  RunGit(['update-index', '--refresh', '-q'], error_ok=True)
   if RunGit(['diff-index', 'HEAD']):
     print 'Cannot %s with a dirty tree.  You must commit locally first.' % cmd
     return 1