rebaseline_server: merge identical results (across multiple builders/configs) into a single row

gm/rebaseline_server/static/constants.js

Index: gm/rebaseline_server/static/constants.js
diff --git a/gm/rebaseline_server/static/constants.js b/gm/rebaseline_server/static/constants.js
index ecca98eae85897e39b0df26e1833aeed7fb8c0e2..8e713112662817395ab38cde46519230c3b5ece2 100644
--- a/gm/rebaseline_server/static/constants.js
+++ b/gm/rebaseline_server/static/constants.js
@@ -74,5 +74,8 @@ module.constant('constants', (function() {
     KEY__EDITS__MODIFICATIONS: 'modifications',
     KEY__EDITS__OLD_RESULTS_HASH: 'oldResultsHash',
     KEY__EDITS__OLD_RESULTS_TYPE: 'oldResultsType',
+
+    // These are just used on the client side, no need to sync with server code.
+    KEY__IMAGEPAIRS__ROWSPAN: 'rowspan',
   }
 })())