Enable ES6 unscopables

src/array.js

 // Copyright 2012 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 declarations have been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 1453 matching lines @@
 
 // -------------------------------------------------------------------
 
 function SetUpArray() {
   %CheckIsBootstrapping();
 
   // Set up non-enumerable constructor property on the Array.prototype
   // object.
   %AddNamedProperty($Array.prototype, "constructor", $Array, DONT_ENUM);
 
+  // Set up unscopable properties on the Array.prototype object.
+  var unscopables = {
+    __proto__: null,
+    copyWithin: true,
+    entries: true,
+    fill: true,
+    find: true,
+    findIndex: true,
+    keys: true,
+    values: true,
+  };
+  %AddNamedProperty($Array.prototype, symbolUnscopables, unscopables,
+      DONT_ENUM | READ_ONLY);
+
   // Set up non-enumerable functions on the Array object.
   InstallFunctions($Array, DONT_ENUM, $Array(
     "isArray", ArrayIsArray
   ));
 
   var specialFunctions = %SpecialArrayFunctions();
 
   var getFunction = function(name, jsBuiltin, len) {
     var f = jsBuiltin;
     if (specialFunctions.hasOwnProperty(name)) {
@@ skipping 48 matching lines @@
   ));
 
   SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush)
   ));
 }
 
 SetUpArray();