Add missing method stub for _GerritCodereviewImpl.

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 and Gerrit."""
 
 from distutils.version import LooseVersion
@@ skipping 2157 matching lines @@
     url = data['revisions'][current_rev]['fetch']['http']['url']
     return gerrit_util.GetChangeDescriptionFromGitiles(url, current_rev)
 
   def UpdateDescriptionRemote(self, description):
     # TODO(tandrii)
     raise NotImplementedError()
 
   def CloseIssue(self):
     gerrit_util.AbandonChange(self._GetGerritHost(), self.GetIssue(), msg='')
 
+  def GetApprovingReviewers(self):
+    """Returns a list of reviewers approving the change.
+
+    Note: not necessarily committers.
+    """
+    raise NotImplementedError()
+
   def SubmitIssue(self, wait_for_merge=True):
     gerrit_util.SubmitChange(self._GetGerritHost(), self.GetIssue(),
                              wait_for_merge=wait_for_merge)
 
   def _GetChangeDetail(self, options=None, issue=None):
     options = options or []
     issue = issue or self.GetIssue()
     assert issue, 'issue required to query Gerrit'
     return gerrit_util.GetChangeDetail(self._GetGerritHost(), str(issue),
                                        options)
@@ skipping 2642 matching lines @@
 if __name__ == '__main__':
   # These affect sys.stdout so do it outside of main() to simplify mocks in
   # unit testing.
   fix_encoding.fix_encoding()
   setup_color.init()
   try:
     sys.exit(main(sys.argv[1:]))
   except KeyboardInterrupt:
     sys.stderr.write('interrupted\n')
     sys.exit(1)