[es5] call ToString() on argument in String.prototype.concat() fast case

test/mjsunit/string-concat.js

+// Copyright 2014 the V8 project authors. All rights reserved.

[arv (Not doing code reviews), 2015/03/23 14:34:45]

15

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function Stringified(toString, valueOf) {

[arv (Not doing code reviews), 2015/03/23 14:34:45]

The test never passes 2 args

+  if (typeof valueOf === "undefined") valueOf = "-" + toString + "-";
+  return {
+    toString: function() { return toString; },
+    valueOf: function() { return valueOf; }
+  };
+}
+
+assertEquals("a.b.", "a.".concat(Stringified("b.")));
+assertEquals("a.b.c.", "a.".concat(Stringified("b."), Stringified("c.")));