Goo.gl ubiquity command

CmdUtils.CreateCommand({
  names: ["Goo.gl", "shorten"],
  description: "Shorten a URL using Google's shortener",
  help: "Just use the url as the parameter",
  author: {
    name: "Jj",
    email: "jjdelc@gmail.com",
    homepage: "http://isgeek.net/",
  },
  license: "GPL",
  homepage: "http://isgeek.net/",
  icon: "http://www.google.com/favicon.ico",
  arguments: [{role: "object", nountype: noun_arb_text, label: "text"}],

  execute: function execute(args) {
    var self = this;
    this._shorten(args.object.text, function(url){
      Utils.clipboard.text = url;
      displayMessage("Copied to clipboard:\n " + url, self);
      return url;
    });
  },
  preview: function preview(pblock, args) {
    pblock.innerHTML = "Generates Goo.gl short url... <i>generating</i>";
    this._shorten(args.object.text, function(url){ 
        pblock.innerHTML = "Replaces " + args.object.html.bold() + " with <b>" + url + "</b>";
    });
  },
  
  _get_endpoint: function(long_url) {
    return 'http://goo.gl/api/shorten?url=' + encodeURIComponent(long_url);
  },

  _shorten: function(long_url, callback) {
    // Code saken from Goo.gl lite Firefox extension
    // https://addons.mozilla.org/en-US/firefox/addon/55308/
    var req = new XMLHttpRequest();
    req.addEventListener("load", function(){
      var response = JSON.parse(req.responseText);
      if (response.error_message){
        return callback("An error occured: " + response.error_message);
      }
      return callback(response.short_url);
    }, false);
    req.addEventListener('error', function(){
      return callback("An error occured:" + res.status);
    }, false);
    req.open("POST", this._get_endpoint(long_url));
    req.setRequestHeader("X-Auth-Google-Url-Shortener", "true");
    req.send();
  }
});