[esnext] prototype runtime implementation for async functions

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index bb38eb8f34d453e76238965cdaad0289376fcedd..cb607920aa7194e16e59aa60fd95e41b4116e126 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -1074,6 +1074,9 @@ class Parser : public ParserBase<ParserTraits> {
   friend class InitializerRewriter;
   void RewriteParameterInitializer(Expression* expr, Scope* scope);
 
+  Expression* EmitCreateJSGeneratorObject(int pos);
+  Expression* EmitYieldJSGeneratorObject(Expression* generator_object);
+
   Scanner scanner_;
   PreParser* reusable_preparser_;
   Scope* original_scope_;  // for ES5 function declarations in sloppy eval