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

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

Index: test/js-perf-test/SixSpeed/classes/es6.js
diff --git a/test/js-perf-test/SixSpeed/classes/es6.js b/test/js-perf-test/SixSpeed/classes/es6.js
new file mode 100644
index 0000000000000000000000000000000000000000..d7ccc87e227ccf29030101f50470974d519f7271
--- /dev/null
+++ b/test/js-perf-test/SixSpeed/classes/es6.js
@@ -0,0 +1,21 @@
+// 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() {}
+}
+
+function ES6() {
+  return new C();
+}