ES6: Add missing Set.prototype.keys function

test/mjsunit/harmony/collection-iterator.js

Index: test/mjsunit/harmony/collection-iterator.js
diff --git a/test/mjsunit/harmony/collection-iterator.js b/test/mjsunit/harmony/collection-iterator.js
index a3a950af3ce72ea7dce7bb95e381d3ba3d9e0701..93113f609205f0fecaafee744b82430eea52dd78 100644
--- a/test/mjsunit/harmony/collection-iterator.js
+++ b/test/mjsunit/harmony/collection-iterator.js
@@ -37,6 +37,11 @@
 })();
 
 
+(function TestSetIteratorKeys() {
+  assertEquals(Set.prototype.keys, Set.prototype.values);
+})();
+
+
 (function TestSetIteratorEntries() {
   var s = new Set;
   s.add(1);