Support rest element pattern with user-defined iterable

src/js/runtime.js

Index: src/js/runtime.js
diff --git a/src/js/runtime.js b/src/js/runtime.js
index eeb887aff4cba2c110cfbe1eddf246e0a1f48db1..c59eceef3876c24c64ec29498a0a6db6c5f87743 100644
--- a/src/js/runtime.js
+++ b/src/js/runtime.js
@@ -23,11 +23,13 @@ var GlobalString = global.String;
 var MakeRangeError;
 var MakeTypeError;
 var speciesSymbol;
+var iteratorSymbol
 
 utils.Import(function(from) {
   MakeRangeError = from.MakeRangeError;
   MakeTypeError = from.MakeTypeError;
   speciesSymbol = from.species_symbol;
+  iteratorSymbol = from.iterator_symbol;
 });
 
 utils.ImportFromExperimental(function(from) {
@@ -67,8 +69,9 @@ function SameValueZero(x, y) {
 }
 
 
-function ConcatIterableToArray(target, iterable) {
+function ConcatIteratorToArray(target, iterator) {
    var index = target.length;
+   var iterable = { [iteratorSymbol]() { return iterator; } };
    for (var element of iterable) {
      AddIndexedProperty(target, index++, element);
    }
@@ -171,7 +174,7 @@ utils.Export(function(to) {
 });
 
 %InstallToContext([
-  "concat_iterable_to_array", ConcatIterableToArray,
+  "concat_iterator_to_array", ConcatIteratorToArray,
 ]);
 
 })