[esnext] prototype runtime implementation for async functions

test/mjsunit/harmony/async-arrow-lexical-super.js

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-await
+
+class BaseClass {
+  constructor(x) {
+    this.name_ = x;
+  }
+  get name() { return this.name_; }
+};
+
+class DeferredSuperCall extends BaseClass {
+  constructor(x) {
+    return async() => super(x);
+  }
+};
+
+assertEqualsAsync(
+  "LexicalSuperCall",
+  new DeferredSuperCall("LexicalSuperCall")().then(x => x.name));
+
+
+class DeferredSuperProperty extends BaseClass {
+  deferredName() { return async() => super.name; }
+};
+
+assertEqualsAsync(
+  "LexicalSuperProperty",
+  new DeferredSuperProperty("LexicalSuperProperty").deferredName()());