Fix ArrayConcat for JSValues/JSFunctions/JSRegExps with @@isConcatSpreadable

test/mjsunit/harmony/array-concat.js

Index: test/mjsunit/harmony/array-concat.js
diff --git a/test/mjsunit/harmony/array-concat.js b/test/mjsunit/harmony/array-concat.js
index d39998d07f6b4b615eabdfef78ddc2c9d1c1f98b..6175989f3ac19026a8453b14ccd0bd4b799c4cf5 100644
--- a/test/mjsunit/harmony/array-concat.js
+++ b/test/mjsunit/harmony/array-concat.js
@@ -304,6 +304,22 @@ function testConcatTypedArray(type, elems, modulo) {
 })();
 
 
+(function testConcatSpreadableStringPrototype() {
+  var str1 = new String("yuck\uD83D\uDCA9")
+  // String wrapper objects are not concat-spreadable by default
+  assertEquals([str1], [].concat(str1));
+
+  String.prototype[Symbol.isConcatSpreadable] = true;
+  // String wrapper objects may be concat-spreadable
+  assertEquals(["y", "u", "c", "k", "\uD83D", "\uDCA9"],
+               [].concat(new String("yuck\uD83D\uDCA9")));
+
+  // String values are never concat-spreadable
+  assertEquals(["yuck\uD83D\uDCA9"], [].concat("yuck\uD83D\uDCA9"));
+  delete String.prototype[Symbol.isConcatSpreadable];
+})();
+
+
 // ES5 tests
 (function testArrayConcatES5() {
   "use strict";