rebaseline_server: use new intermediate JSON format

gm/rebaseline_server/imagepairset_test.py

 #!/usr/bin/python
 
 """
 Copyright 2014 Google Inc.
 
 Use of this source code is governed by a BSD-style license that can be
 found in the LICENSE file.
 
 Test imagepairset.py
 """
@@ skipping 67 matching lines @@
 
   def test_success(self):
     """Assembles some ImagePairs into an ImagePairSet, and validates results.
     """
     image_pairs = [
         MockImagePair(base_url=BASE_URL_1, dict_to_return=IMAGEPAIR_1_AS_DICT),
         MockImagePair(base_url=BASE_URL_1, dict_to_return=IMAGEPAIR_2_AS_DICT),
         MockImagePair(base_url=BASE_URL_1, dict_to_return=IMAGEPAIR_3_AS_DICT),
     ]
     expected_imageset_dict = {
-        'columnHeaders': {
+        'extraColumnHeaders': {
             'builder': {
                 'headerText': 'builder',
                 'isFilterable': True,
                 'isSortable': True,
                 'valuesAndCounts': {
                     'MyBuilder': 3
                 },
             },
             'test': {
                 'headerText': 'which GM test',
@@ skipping 65 matching lines @@
     return self._dict_to_return
 
 
 def main():
   suite = unittest.TestLoader().loadTestsFromTestCase(ImagePairSetTest)
   unittest.TextTestRunner(verbosity=2).run(suite)
 
 
 if __name__ == '__main__':
   main()