[es6] correct constant_elements backing-store when spread is used

test/mjsunit/harmony/spread-array.js

Index: test/mjsunit/harmony/spread-array.js
diff --git a/test/mjsunit/harmony/spread-array.js b/test/mjsunit/harmony/spread-array.js
index 18b72a28c5ab24301625f45c7b5af4979aff6bd6..6f116a592c48b1c0b27f91fe5388428cae66c9b9 100644
--- a/test/mjsunit/harmony/spread-array.js
+++ b/test/mjsunit/harmony/spread-array.js
@@ -11,6 +11,12 @@
 
   assertArrayEquals(['a', 'b', 'c', 'd', 'e', 'f'],
                     ['a', ...'bc', 'd', ...'ef'])
+  assertEquals([1, 2, 3], [1, 2, ...[3]]);
+  assertEquals([1, 2, , 3, 4, 5], [1, 2, ,...[3], 4, 5]);
+  assertEquals(['a', 'b', 'c'], ['a', 'b', ...['c']]);
+  assertEquals(['a', 'b', ,'c', 'd', 'e'], ['a', 'b', , ...['c'],'d', 'e']);
+  assertEquals([{a: true},{b: false},{c: true},{d: false}],
+               [{a: true},{b: false},...[{c: true}],{d: false}]);
 })();