Add spread call micro-benchmarks.

test/js-perf-test/SixSpeed/run.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.
+
+load('benchmark.js');
+load('traceur-runtime.js');
+
+function benchTest(test, type, fn) {
+  var name = test + '-' + type;
+  var bench = new Benchmark(name, fn);
+  bench.on('complete', function() {
+    print(name + '(Score): ' + bench.count);
+  });
+  bench.options.maxTime = 1;
+  bench.run();
+}
+
+load('spread/spread__es5.js');
+load('spread/spread__es6.js');
+load('spread/spread__traceur.js');