[es7] Implement async functions parsing

src/runtime/runtime-function.cc

Index: src/runtime/runtime-function.cc
diff --git a/src/runtime/runtime-function.cc b/src/runtime/runtime-function.cc
index f994ee336561a3c51da186de4783480b75bf0a92..b2842cbcb6911b0ce7ba25f6db7d0aa4d546fb1e 100644
--- a/src/runtime/runtime-function.cc
+++ b/src/runtime/runtime-function.cc
@@ -105,6 +105,14 @@ RUNTIME_FUNCTION(Runtime_FunctionGetSourceCode) {
 }
 
 
+RUNTIME_FUNCTION(Runtime_FunctionIsAsync) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 1);
+  CONVERT_ARG_CHECKED(JSFunction, f, 0);
+  return isolate->heap()->ToBoolean(f->shared()->is_async());
+}
+
+
 RUNTIME_FUNCTION(Runtime_FunctionGetScriptSourcePosition) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 1);