The ArrayConcat builtin didn't respect @@isConcatSp

test/mjsunit/harmony/array-concat.js

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --harmony-concat-spreadable
 
 (function testArrayConcatArity() {
   "use strict";
   assertEquals(1, Array.prototype.concat.length);
 })();
@@ skipping 688 matching lines @@
   arr3.length = 10000;
   for (var i = 0; i < 100; i++) {
     Object.defineProperty(arr3, i * i, {get: mkGetter(i)});
     expectedTrace[i] = i;
     expectedTrace[100 + i] = i;
   }
   var r4 = [0].concat(arr3, arr3);
   assertEquals(1 + arr3.length * 2, r4.length);
   assertEquals(expectedTrace, trace);
 })();
+
+
+(function testConcatArrayNonSpreadable() {
+  "use strict";
+  var b = [];
+  b[Symbol.isConcatSpreadable] = false;
+  assertEquals(2, b.concat(b).length);
+  assertEquals(1, [].concat(b).length);
+  assertEquals(1, [].concat(b, new Array).length);
+  assertEquals(2, [].concat(b, new Object).length);
+})();