Update harmony Object.prototype.toString to 2/2/2015 spec

src/harmony-tostring.js

 // Copyright 2013 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.
 
 "use strict";
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js and symbol.js:
 // var $Object = global.Object;
 // var $Symbol = global.Symbol;
 
-var kBuiltinStringTags = {
-  "__proto__": null,
-  "Arguments": true,
-  "Array": true,
-  "Boolean": true,
-  "Date": true,
-  "Error": true,
-  "Function": true,
-  "Number": true,
-  "RegExp": true,
-  "String": true
-};
-
 DefaultObjectToString = ObjectToStringHarmony;
 // ES6 draft 08-24-14, section 19.1.3.6
 function ObjectToStringHarmony() {
   if (IS_UNDEFINED(this) && !IS_UNDETECTABLE(this)) return "[object Undefined]";
   if (IS_NULL(this)) return "[object Null]";
   var O = ToObject(this);
   var builtinTag = %_ClassOf(O);
   var tag = O[symbolToStringTag];
-  if (IS_UNDEFINED(tag)) {
+  if (!IS_STRING(tag)) {
     tag = builtinTag;
-  } else if (!IS_STRING(tag)) {
-    return "[object ???]";
-  } else if (tag !== builtinTag && kBuiltinStringTags[tag]) {
-    return "[object ~" + tag + "]";
   }
   return "[object " + tag + "]";
 }
 
 function HarmonyToStringExtendSymbolPrototype() {
   %CheckIsBootstrapping();
 
   InstallConstants($Symbol, $Array(
     // TODO(dslomov, caitp): Move to symbol.js when shipping
    "toStringTag", symbolToStringTag
@@ skipping 14 matching lines @@
   // Set up the non-enumerable functions on the Array prototype object.
   var desc = ToPropertyDescriptor({
     value: ObjectToStringHarmony
   });
   DefineOwnProperty($Object.prototype, "toString", desc, false);
 
   %ToFastProperties($Object.prototype);
 }
 
 HarmonyToStringExtendObjectPrototype();