code: function (debug) {
    this.debug = debug;
    this.files = {};
    this.resolvers = [this.httpResolver, this.nullResolver];
    this.contentRetrievers = {
      'http': this.xhrRetriever,
      'https': this.xhrRetriever,
      'chrome-extension': this.xhrRetriever,
      'resource': this.xhrRetriever,
      'chrome': this.xhrRetriever,
      'app': this.xhrRetriever,
      'gopher': this.xhrRetriever,  // For Cordova; see http://crbug.com/513352 .
      'manifest': this.manifestRetriever
    };
  }
docs: The Resource registry for FreeDOM.  Used to look up requested Resources,
  and provide lookup and migration of resources.
  @Class Resource
  @param {Debug} debug The logger to use for debugging.
  @constructor