catapult/dashboard/dashboard/elements/xhr-element.html

<polymer-element name="xhr-element">
  <script>
    Polymer('xhr-element', {
      LOGIN_ERROR_MESSAGE: 'Please check if you are logged in with a ' +
                           'google.com or chromium.org account in the ' +
                           'upper right corner of the page.',
      handleError: function(req, callback) {
        callback(this.LOGIN_ERROR_MESSAGE);
      },
      handleLoad: function(req, loadCallback, errorCallback) {
        if (req.status != 200) {
          errorCallback('HTTP error ' + req.status);
          return;
        }
        try {
          var response = JSON.parse(req.responseText);
        } catch (e) {
          errorCallback(this.LOGIN_ERROR_MESSAGE);
          return;
        }
        if (response.error) {
          errorCallback(response.error);
          return;
        }
        loadCallback(response);
      },
      send: function(url, xsrfToken, params, loadCallback, errorCallback) {
        var postdata = 'xsrf_token=' + encodeURIComponent(xsrfToken);
        for (var name in params) {
          postdata += '&' + name + '=' + encodeURIComponent(params[name]);
        }
        var req = new XMLHttpRequest();
        req.onerror = this.handleError.bind(this, req, errorCallback);
        req.onload = this.handleLoad.bind(this, req, loadCallback, errorCallback);
        req.open('post', url, true);
        req.setRequestHeader('Content-type',
                             'application/x-www-form-urlencoded');
        req.send(postdata);
        return req;
      }
    });
  </script>
</polymer-element>