[WIP] PluginPrivateFileSystem example (won't commit)

ppapi/examples/pluginfs/pluginfs.js

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 function StartRequest() {
   var plugin = document.getElementById("plugin");
   var filename = document.getElementById("filename").value;
   plugin.postMessage(filename);
 }
 
 function HandleMessage(message_event) {
   document.getElementById("content").value = message_event.data;
 }
 
 document.addEventListener('DOMContentLoaded', function () {
   // Attach a listener for the message event. This must happen after the plugin
   // object was created.
   document.getElementById("plugin")
       .addEventListener("message", HandleMessage, false);
 
   document.getElementById("start")
       .addEventListener("click", StartRequest, false);
 });