Use proper ToLength() operation in %ArrayConcat()

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 738c81a45753d44653f0e0e6aabf6c4fbde4e4d0..1ab2dc28ac41b7d8db35d3f6d437ff52e818954f 100644
--- a/test/mjsunit/harmony/array-concat.js
+++ b/test/mjsunit/harmony/array-concat.js
@@ -40,6 +40,40 @@
 })();
 
 
+(function testConcatArrayLikeStringLength() {
+  "use strict";
+  var obj = {
+    "length": "6",
+    "1": "A",
+    "3": "B",
+    "5": "C"
+  };
+  obj[Symbol.isConcatSpreadable] = true;
+  var obj2 = { length: 3, "0": "0", "1": "1", "2": "2" };
+  var arr = ["X", "Y", "Z"];
+  assertEquals([void 0, "A", void 0, "B", void 0, "C",
+               { "length": 3, "0": "0", "1": "1", "2": "2" },
+               "X", "Y", "Z"], Array.prototype.concat.call(obj, obj2, arr));
+})();
+
+
+(function testConcatArrayLikeToLengthThrows() {
+  "use strict";
+  var obj = {
+    "length": {valueOf: null, toString: null},
+    "1": "A",
+    "3": "B",
+    "5": "C"
+  };
+  obj[Symbol.isConcatSpreadable] = true;
+  var obj2 = { length: 3, "0": "0", "1": "1", "2": "2" };
+  var arr = ["X", "Y", "Z"];
+  assertThrows(function() {
+    Array.prototype.concat.call(obj, obj2, arr);
+  }, TypeError);
+})();
+
+
 (function testConcatHoleyArray() {
   "use strict";
   var arr = [];