[esnext] prototype runtime implementation for async functions

src/builtins.cc

Index: src/builtins.cc
diff --git a/src/builtins.cc b/src/builtins.cc
index ed07d5d089101311f1f90c61b396e6ba61de64ca..842507bd0f6459182e73cad0256086d393588b45 100644
--- a/src/builtins.cc
+++ b/src/builtins.cc
@@ -2487,6 +2487,17 @@ void Builtins::Generate_GeneratorPrototypeThrow(CodeStubAssembler* assembler) {
                                     "[Generator].prototype.throw");
 }
 
+void Builtins::Generate_AsyncFunctionNext(CodeStubAssembler* assembler) {
+  Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kNext,
+                                    "AsyncFunctionNext");
+}
+
+// ES6 section 25.3.1.4 Generator.prototype.throw ( exception )
+void Builtins::Generate_AsyncFunctionThrow(CodeStubAssembler* assembler) {
+  Generate_GeneratorPrototypeResume(assembler, JSGeneratorObject::kThrow,
+                                    "AsyncFunctionThrow");
+}
+
 // -----------------------------------------------------------------------------
 // ES6 section 26.1 The Reflect Object
 
@@ -4212,6 +4223,13 @@ BUILTIN(GeneratorFunctionConstructor) {
   return *result;
 }
 
+BUILTIN(AsyncFunctionConstructor) {
+  HandleScope scope(isolate);
+  Handle<JSFunction> result;
+  ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
+      isolate, result, CreateDynamicFunction(isolate, args, "async function"));
+  return *result;
+}
 
 // ES6 section 19.4.1.1 Symbol ( [ description ] ) for the [[Call]] case.
 BUILTIN(SymbolConstructor) {