Don't take iterable path in ArrayFrom if items[@@iterator] is null

src/harmony-array.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:
 // var $Array = global.Array;
 
@@ skipping 124 matching lines @@
   if (mapping) {
     if (!IS_SPEC_FUNCTION(mapfn)) {
       throw MakeTypeError('called_non_callable', [ mapfn ]);
     } else if (IS_NULL_OR_UNDEFINED(receiver)) {
       receiver = %GetDefaultReceiver(mapfn) || receiver;
     } else if (!IS_SPEC_OBJECT(receiver) && %IsSloppyModeFunction(mapfn)) {
       receiver = ToObject(receiver);
     }
   }
 
-  var iterable = ToIterable(items);
+  var iterable = GetMethod(items, symbolIterator);

[arv (Not doing code reviews), 2015/01/21 15:05:18]

We now call items.[[Get]](symbolIterator) twice. The spec mandates that it is
only called once. The spec makes me sad that we cannot use for-of loop here.

[caitp (gmail), 2015/01/21 17:21:49]

hmm, well it's trivial to replace the for...of with a more explicit loop, but
that is a bit sad.

   var k;
   var result;
   var mappedValue;
   var nextValue;
 
   if (!IS_UNDEFINED(iterable)) {
     result = %IsConstructor(this) ? new this() : [];
 
     k = 0;
     for (nextValue of items) {
@@ skipping 59 matching lines @@
 
   // Set up the non-enumerable functions on the Array prototype object.
   InstallFunctions($Array.prototype, DONT_ENUM, $Array(
     "find", ArrayFind,
     "findIndex", ArrayFindIndex,
     "fill", ArrayFill
   ));
 }
 
 HarmonyArrayExtendArrayPrototype();