[esnext] prototype runtime implementation for async functions

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 9cebd3f1b470e8e743d163ee17fe69040445a113..7d1251e0b4f0c688a03df25e6f5978456876db4a 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -1227,6 +1227,7 @@ Handle<JSFunction> Factory::NewFunction(Handle<Map> map,
       map.is_identical_to(
           isolate()->sloppy_function_with_readonly_prototype_map()) ||
       map.is_identical_to(isolate()->strict_function_map()) ||
+      map.is_identical_to(isolate()->strict_function_without_prototype_map()) ||
       // TODO(titzer): wasm_function_map() could be undefined here. ugly.
       (*map == context->get(Context::WASM_FUNCTION_MAP_INDEX)) ||
       map.is_identical_to(isolate()->proxy_function_map()));
@@ -1660,7 +1661,7 @@ void Factory::NewJSArrayStorage(Handle<JSArray> array,
 
 Handle<JSGeneratorObject> Factory::NewJSGeneratorObject(
     Handle<JSFunction> function) {
-  DCHECK(function->shared()->is_generator());
+  DCHECK(function->shared()->is_generator() || function->shared()->is_async());
   JSFunction::EnsureHasInitialMap(function);
   Handle<Map> map(function->initial_map());
   DCHECK_EQ(JS_GENERATOR_OBJECT_TYPE, map->instance_type());
@@ -2066,6 +2067,9 @@ Handle<SharedFunctionInfo> Factory::NewSharedFunctionInfo(
     shared->set_instance_class_name(isolate()->heap()->Generator_string());
     shared->DisableOptimization(kGenerator);
   }
+  if (IsAsyncFunction(kind)) {
+    shared->DisableOptimization(kGenerator);
+  }
   return shared;
 }