The ArrayConcat builtin didn't respect @@isConcatSp

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 71b6790bc7b13e238930ed824d165d76ec903c2c..87bd246cbad7381d42f2a8c2ca294aa9023d0c61 100644
--- a/test/mjsunit/harmony/array-concat.js
+++ b/test/mjsunit/harmony/array-concat.js
@@ -706,3 +706,14 @@ function testConcatTypedArray(type, elems, modulo) {
   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);
+})();