WIP [esnext] implement async iteration proposal

src/runtime/runtime-internal.cc

Index: src/runtime/runtime-internal.cc
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index d9113753d03b2b20b1cdb86348bbd1eacdae7969..6e6445c85bc6fa0ea25610276f99943fa765f463 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -224,6 +224,13 @@ RUNTIME_FUNCTION(Runtime_ThrowSymbolIteratorInvalid) {
       isolate, NewTypeError(MessageTemplate::kSymbolIteratorInvalid));
 }
 
+RUNTIME_FUNCTION(Runtime_ThrowSymbolAsyncIteratorInvalid) {
+  HandleScope scope(isolate);
+  DCHECK(args.length() == 0);
+  THROW_NEW_ERROR_RETURN_FAILURE(
+      isolate, NewTypeError(MessageTemplate::kSymbolAsyncIteratorInvalid));
+}
+
 RUNTIME_FUNCTION(Runtime_ThrowNotGeneric) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());
@@ -494,5 +501,20 @@ RUNTIME_FUNCTION(Runtime_Typeof) {
   return *Object::TypeOf(isolate, object);
 }
 
+RUNTIME_FUNCTION(Runtime_CreateAsyncFromSyncIterator) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+
+  CONVERT_ARG_HANDLE_CHECKED(Object, sync_iterator, 0);
+
+  if (!sync_iterator->IsJSReceiver()) {
+    THROW_NEW_ERROR_RETURN_FAILURE(
+        isolate, NewTypeError(MessageTemplate::kSymbolIteratorInvalid));
+  }
+
+  return *isolate->factory()->NewJSAsyncFromSyncIterator(
+      Handle<HeapObject>::cast(sync_iterator));
+}
+
 }  // namespace internal
 }  // namespace v8