[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 71d7059bf8bccf790fcdf346a7f4c8bea729cbef..3a8c06bf55040830b18da57297a71c368b62abbe 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<FixedArray> operand_stack;
   if (FLAG_ignition && FLAG_ignition_generators) {
@@ -46,7 +47,8 @@ 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());