rename rebaseline_server JSON constants to be more consistent

gm/rebaseline_server/compare_rendered_pictures.py

Index: gm/rebaseline_server/compare_rendered_pictures.py
diff --git a/gm/rebaseline_server/compare_rendered_pictures.py b/gm/rebaseline_server/compare_rendered_pictures.py
index ba621c3a35dabdb3a68c62951d6b2be8f95b1a8c..75a80d4de2704afc527c2ad7aa1834ac61f4888d 100755
--- a/gm/rebaseline_server/compare_rendered_pictures.py
+++ b/gm/rebaseline_server/compare_rendered_pictures.py
@@ -108,13 +108,13 @@ class RenderedPicturesComparisons(results.BaseComparisons):
         diff_base_url=self._diff_base_url)
 
     all_image_pairs.ensure_extra_column_values_in_summary(
-        column_id=results.KEY__EXTRACOLUMN__RESULT_TYPE, values=[
+        column_id=results.KEY__EXTRACOLUMNS__RESULT_TYPE, values=[
             results.KEY__RESULT_TYPE__FAILED,
             results.KEY__RESULT_TYPE__NOCOMPARISON,
             results.KEY__RESULT_TYPE__SUCCEEDED,
         ])
     failing_image_pairs.ensure_extra_column_values_in_summary(
-        column_id=results.KEY__EXTRACOLUMN__RESULT_TYPE, values=[
+        column_id=results.KEY__EXTRACOLUMNS__RESULT_TYPE, values=[
             results.KEY__RESULT_TYPE__FAILED,
             results.KEY__RESULT_TYPE__NOCOMPARISON,
         ])
@@ -164,7 +164,7 @@ class RenderedPicturesComparisons(results.BaseComparisons):
           if imagepair:
             all_image_pairs.add_image_pair(imagepair)
             result_type = imagepair.extra_columns_dict\
-                [results.KEY__EXTRACOLUMN__RESULT_TYPE]
+                [results.KEY__EXTRACOLUMNS__RESULT_TYPE]
             if result_type != results.KEY__RESULT_TYPE__SUCCEEDED:
               failing_image_pairs.add_image_pair(imagepair)
 
@@ -231,13 +231,13 @@ class RenderedPicturesComparisons(results.BaseComparisons):
       result_type = results.KEY__RESULT_TYPE__FAILED
 
     extra_columns_dict = {
-        results.KEY__EXTRACOLUMN__CONFIG: config,
-        results.KEY__EXTRACOLUMN__RESULT_TYPE: result_type,
-        results.KEY__EXTRACOLUMN__TEST: test,
+        results.KEY__EXTRACOLUMNS__CONFIG: config,
+        results.KEY__EXTRACOLUMNS__RESULT_TYPE: result_type,
+        results.KEY__EXTRACOLUMNS__TEST: test,
         # TODO(epoger): Right now, the client UI crashes if it receives
         # results that do not include this column.
         # Until we fix that, keep the client happy.
-        results.KEY__EXTRACOLUMN__BUILDER: 'TODO',
+        results.KEY__EXTRACOLUMNS__BUILDER: 'TODO',
     }
 
     try: