[async-iteration] implement Async-from-Sync Iterator

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 71882859c0eea5ed03c13413945af35a6d98ce45..8d90299a428eec914f1c0717a471ac1f1f93eef9 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1958,6 +1958,16 @@ Handle<JSIteratorResult> Factory::NewJSIteratorResult(Handle<Object> value,
   return js_iter_result;
 }
 
+Handle<JSAsyncFromSyncIterator> Factory::NewJSAsyncFromSyncIterator(
+    Handle<HeapObject> sync_iterator) {
+  Handle<Map> map(isolate()->native_context()->async_from_sync_iterator_map());
+  Handle<JSAsyncFromSyncIterator> iterator =
+      Handle<JSAsyncFromSyncIterator>::cast(NewJSObjectFromMap(map));
+
+  iterator->set_sync_iterator(*sync_iterator);
+  return iterator;
+}
+
 Handle<JSMap> Factory::NewJSMap() {
   Handle<Map> map(isolate()->native_context()->js_map_map());
   Handle<JSMap> js_map = Handle<JSMap>::cast(NewJSObjectFromMap(map));