Run jshint over all JavaScript files

ports/devenv/devenvwidget/demo.js

 /*
  * Copyright (c) 2014 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+/* globals DevEnvWidget */
+
+'use strict';
+
 // This is an example use of devenvwidget.js.
 function $(i) {
   return document.querySelector(i);
 }
 document.addEventListener('DOMContentLoaded', function() {
   var devenv = new DevEnvWidget({
     source: $('#source'),
     run: $('#run'),
     status: $('#status'),
     output: $('#output')
   });
 });