[runtime] Avoid @@isConcatSpreadable lookup for fast path Array.prototype.concat

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..02383f5b2c2d48a0081b2aaf64097223f304dd7a 100644
--- a/test/mjsunit/harmony/array-concat.js
+++ b/test/mjsunit/harmony/array-concat.js
@@ -22,6 +22,15 @@
   assertEquals(false, desc.enumerable);
 })();
 
+(function testNonConcatSpreadableArray() {
+  "use strict"
+  var array = [1, 2, 3];
+  assertEquals(array, [].concat(array));
+  assertEquals(array, array.concat([]));
+  array[Symbol.isConcatSpreadable] = false;
+  assertEquals([[1,2,3]], [].concat(array));
+  assertEquals([[1,2,3]], array.concat([]));
+})();
 
 (function testConcatArrayLike() {
   "use strict";