bench: add process.nextTick() benchmark

benchmark/next-tick.js

@@ -0,0 +1,17 @@
+// run with `time node benchmark/next-tick.js`
+var assert = require('assert');
+
+var N = 1e7;
+var n = 0;
+
+process.on('exit', function() {
+  assert.equal(n, N);
+});
+
+function cb() {
+  n++;
+}
+
+for (var i = 0; i < N; ++i) {
+  process.nextTick(cb);
+}