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..fe452fed8e1a75f0e8b8e7c7c5c84cf3c2c323c3 100644
--- a/src/runtime/runtime-generator.cc
+++ b/src/runtime/runtime-generator.cc
@@ -69,6 +69,27 @@ RUNTIME_FUNCTION(Runtime_GeneratorGetInputOrDebugPos) {
   return generator->input_or_debug_pos();
 }
 
+RUNTIME_FUNCTION(Runtime_GeneratorGetAwaitInput) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator, 0);
+
+  return generator->await_input();
+}
+
+RUNTIME_FUNCTION(Runtime_GeneratorSaveInputForAwait) {
+  HandleScope scope(isolate);
+  DCHECK_EQ(1, args.length());
+  CONVERT_ARG_HANDLE_CHECKED(JSGeneratorObject, generator, 0);
+
+  // Generator must be executing
+  DCHECK_EQ(generator->continuation(), JSGeneratorObject::kGeneratorExecuting);
+
+  generator->set_await_input(generator->input_or_debug_pos());
+
+  return isolate->heap()->undefined_value();
+}
+
 RUNTIME_FUNCTION(Runtime_GeneratorGetResumeMode) {
   HandleScope scope(isolate);
   DCHECK_EQ(1, args.length());