function(){
 var twitterWidgets = document.createElement('script');
 twitterWidgets.type = 'text/javascript';
 twitterWidgets.async = true;
 twitterWidgets.src = 'http://platform.twitter.com/widgets.js';
 // Setup a callback to track once the script loads.
 twitterWidgets.onload = _ga.trackTwitter;
 document.getElementsByTagName('head')[0].appendChild(twitterWidgets);
 }