[esnext] prototype runtime implementation for async functions

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 eeac3ad6b64b934b897387313139d88ccaa6eb4e..1a94cb45d04b6ae7382859f6c88c154f6d1e1d78 100644
--- a/src/runtime/runtime-generator.cc
+++ b/src/runtime/runtime-generator.cc
@@ -17,7 +17,8 @@ RUNTIME_FUNCTION(Runtime_CreateJSGeneratorObject) {
   DCHECK(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSFunction, function, 0);
   CONVERT_ARG_HANDLE_CHECKED(Object, receiver, 1);
-  RUNTIME_ASSERT(function->shared()->is_generator());
+  RUNTIME_ASSERT(function->shared()->is_generator() ||
+                 function->shared()->is_async());
 
   Handle<JSGeneratorObject> generator =
       isolate->factory()->NewJSGeneratorObject(function);
@@ -37,7 +38,8 @@ RUNTIME_FUNCTION(Runtime_SuspendJSGeneratorObject) {
 
   JavaScriptFrameIterator stack_iterator(isolate);
   JavaScriptFrame* frame = stack_iterator.frame();
-  RUNTIME_ASSERT(frame->function()->shared()->is_generator());
+  RUNTIME_ASSERT(frame->function()->shared()->is_generator() ||
+                 frame->function()->shared()->is_async());
   DCHECK_EQ(frame->function(), generator_object->function());
   DCHECK(frame->function()->shared()->is_compiled());
   DCHECK(!frame->function()->IsOptimized());