Enable ES6 unscopables

src/unscopables.js

-// Copyright 2014 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.
-// var $Array = global.Array;
-// var $Symbol = global.Symbol;
-
-function UnscopablesExtendSymbol() {
-  %CheckIsBootstrapping();
-  InstallConstants($Symbol, $Array(
-    "unscopables", symbolUnscopables
-  ));
-}
-
-UnscopablesExtendSymbol();
-
-
-var arrayUnscopables = {
-  __proto__: null,
-  copyWithin: true,
-  entries: true,
-  fill: true,
-  find: true,
-  findIndex: true,
-  keys: true,
-  values: true,
-};
-
-
-function UnscopablesExtendArrayPrototype() {
-  %CheckIsBootstrapping();
-  %AddNamedProperty($Array.prototype, symbolUnscopables, arrayUnscopables,
-                    DONT_ENUM | READ_ONLY);
-}
-
-UnscopablesExtendArrayPrototype();