WIP [esnext] implement async iteration proposal

src/runtime/runtime-generator.cc

Index: src/runtime/runtime-generator.cc
diff --git a/src/runtime/runtime-generator.cc b/src/runtime/runtime-generator.cc
index 81c66408d363955522d998639132ba848d52dcfe..fb756ac65be5dc41c59391c26f29a27110190a9e 100644
--- a/src/runtime/runtime-generator.cc
+++ b/src/runtime/runtime-generator.cc
@@ -69,6 +69,14 @@ RUNTIME_FUNCTION(Runtime_GeneratorGetInputOrDebugPos) {
   return generator->input_or_debug_pos();
 }
 
+RUNTIME_FUNCTION(Runtime_AsyncGeneratorGetAwaitInput) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSAsyncGeneratorObject, generator, 0);
+
+  return generator->await_input();
+}
+
 RUNTIME_FUNCTION(Runtime_GeneratorGetResumeMode) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());