[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 9466ab7d3a727c2fe12d70ac977df0b0cac57f35..c0fc2881ae05eaf19276f22e51b37aa26635dc5e 100644
--- a/src/d8.cc
+++ b/src/d8.cc
@@ -887,6 +887,10 @@ 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);
@@ -1204,6 +1208,11 @@ 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;
 }