[js-perf-tests] Add super benchmarks from SixSpeed.

test/js-perf-test/SixSpeed/super/es6.js

+// Copyright 2017 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.
+
+// This benchmark is based on the six-speed benchmark build output.
+// Copyright 2014 Kevin Decker <https://github.com/kpdecker/six-speed/>
+
+new BenchmarkSuite('ES6', [1000], [
+  new Benchmark('ES6', false, false, 0, ES6),
+]);
+
+class C {
+  constructor() {
+    this.foo = 'bar';
+  }
+  bar() {
+    return 41;
+  }
+}
+
+class D extends C {
+  constructor() {
+    super();
+    this.baz = 'bat';
+  }
+  bar() {
+    return super.bar() + 1;
+  }
+}
+
+function ES6() {
+  var d = new D();
+  return d.bar();
+}