benchmarks: add spread operator benchmark

Useful for comparing spread operator performance over time.

benchmark/es/spread-bench.js

@@ -0,0 +1,59 @@
+'use strict';
+
+const common = require('../common.js');
+const assert = require('assert');
+
+const bench = common.createBenchmark(main, {
+  method: ['apply', 'spread', 'call-spread'],
+  count: [5, 10, 20],
+  context: ['context', 'null'],
+  rest: [0, 1],
+  millions: [5]
+});
+
+function makeTest(count, rest) {
+  if (rest) {
+    return function test(...args) {
+      assert.strictEqual(count, args.length);
+    };
+  } else {
+    return function test() {
+      assert.strictEqual(count, arguments.length);
+    };
+  }
+}
+
+function main(conf) {
+  const n = +conf.millions * 1e6;
+  const ctx = conf.context === 'context' ? {} : null;
+  var fn = makeTest(conf.count, conf.rest);
+  const args = new Array(conf.count);
+  var i;
+  for (i = 0; i < conf.count; i++)
+    args[i] = i;
+
+  switch (conf.method) {
+    case 'apply':
+      bench.start();
+      for (i = 0; i < n; i++)
+        fn.apply(ctx, args);
+      bench.end(n / 1e6);
+      break;
+    case 'spread':
+      if (ctx !== null)
+        fn = fn.bind(ctx);
+      bench.start();
+      for (i = 0; i < n; i++)
+        fn(...args);
+      bench.end(n / 1e6);
+      break;
+    case 'call-spread':
+      bench.start();
+      for (i = 0; i < n; i++)
+        fn.call(ctx, ...args);
+      bench.end(n / 1e6);
+      break;
+    default:
+      throw new Error('Unexpected method');
+  }
+}