Add a simple benchmark for Navigator.handlePage (#926)

I'm going to do some hacking around in here and I want to make sure I don't
hork performance.  Don't have a harness for this or anything yet.  Mostly just
pushing it up so I don't lose track of it.

packages/react-server/core/__bench__/handlePage.js

@@ -0,0 +1,40 @@
+import {Suite}              from "benchmark";
+import Navigator            from "../context/Navigator.js";
+import ExpressServerRequest from "../ExpressServerRequest.js";
+import RequestLocalStorage  from "../util/RequestLocalStorage.js";
+
+class Middleware {
+	handleRoute        (next){return next()};
+	getHeaders         (next){return next()};
+	getTitle           (next){return next()};
+	getScripts         (next){return next()};
+	getHeadStylesheets (next){return next()};
+	getMetaTags        (next){return next()};
+	getLinkTags        (next){return next()};
+	getBase            (next){return next()};
+	getBodyClasses     (next){return next()};
+	getElements        (next){return next()};
+}
+
+function run (n) {
+	const m         = new Array(n).join(".").split(".").map(() => Middleware);
+	const navigator = new Navigator({}, {routes: {}});
+	const request   = new ExpressServerRequest({ query: {} })
+
+	class Page extends Middleware { static middleware() {return m} }
+
+	return function (deferred) {
+		navigator.once('navigateDone', function() { deferred.resolve() });
+		RequestLocalStorage.startRequest(() => {
+			navigator.handlePage(Page, request, "pageload");
+		});
+	}
+}
+
+new Suite()
+	.add("1",    run(   1), { defer: true })
+	.add("10",   run(  10), { defer: true })
+	.add("100",  run( 100), { defer: true })
+	.add("1000", run(1000), { defer: true })
+	.on('cycle', (v) => console.log(v.target.name + "\t" + v.target.stats.mean))
+	.run()

packages/react-server/package.json

@@ -49,6 +49,7 @@
     "babel-preset-es2015": "^6.18.0",
     "babel-preset-react": "^6.16.0",
     "babel-preset-stage-1": "^6.16.0",
+    "benchmark": "^2.1.4",
     "cheerio": "^0.22.0",
     "eslint": "^3.8.1",
     "eslint-plugin-react": "^6.4.1",