[js-perf-test] Add a basic async-await microbenchmark

test/js-perf-test/AsyncAwait/native.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.
+
+
+new BenchmarkSuite('Native', [1000], [
+  new Benchmark('Basic', false, false, 0, Basic, Setup),
+]);
+
+var a,b,c,d,e,f,g,h,i,j,x;
+
+function Setup() {
+  x = Promise.resolve();
+
+  j = async function j() { return x; };
+  i = async function i() {
+    await j();
+    await j();
+    await j();
+    await j();
+    await j();
+    await j();
+    await j();
+    await j();
+    await j();
+    return j();
+  };
+  h = async function h() { return i(); };
+  g = async function g() { return h(); };
+  f = async function f() { return g(); };
+  e = async function e() { return f(); };
+  d = async function d() { return e(); };
+  c = async function c() { return d(); };
+  b = async function b() { return c(); };
+  a = async function a() { return b(); };
+
+  %RunMicrotasks();
+}
+
+function Basic() {
+  a();
+  %RunMicrotasks();
+}