[esnext] prototype runtime implementation for async functions

src/d8.cc

Index: src/d8.cc
diff --git a/src/d8.cc b/src/d8.cc
index 169bc263934a8f1344419ac53ee0d88b8431d50f..0dd1ed8d66464ce84f18480b7316c25594d050da 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -886,6 +886,10 @@ void Shell::Version(const v8::FunctionCallbackInfo<v8::Value>& args) {
                           NewStringType::kNormal).ToLocalChecked());
 }
 
+void Shell::FlushMicrotasks(const v8::FunctionCallbackInfo<v8::Value>& args) {
+  Isolate* isolate = args.GetIsolate();
+  isolate->RunMicrotasks();
+}
 
 void Shell::ReportException(Isolate* isolate, v8::TryCatch* try_catch) {
   HandleScope handle_scope(isolate);
@@ -1203,6 +1207,11 @@ Local<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
           .ToLocalChecked(),
       os_templ);
 
+  global_template->Set(
+      String::NewFromUtf8(isolate, "flushMicrotasks", NewStringType::kNormal)
+          .ToLocalChecked(),
+      FunctionTemplate::New(isolate, FlushMicrotasks));
+
   return global_template;
 }