Implementation of the A / B test on Google Analytics with the old Analytics tag (ga.js)

Implementing A / B test tracking requires updating the Google Analytics script. 
The operation consists of entering a custom variable with the value "yes" or "no" depending on whether the page is optimized or not.

Adding the custom variable

Here is the tag to add between _gaq.push(['_setAccount'and_gaq.push(['trackPageViews']);

var _gaq = _gaq || [];

_gaq.push(['_setAccount', 'UA-XXXXXXXX-1']);

// Début du code à copier-coller

var cookie = document.cookie;

if (cookie.indexOf('fstrz=') !== -1) {
  _gaq.push(['_setCustomVar', 5, 'Fasterize', cookie.indexOf('fstrz=true') !== -1 ? 'yes' : 'no', 2]);
} else {
  _gaq.push(['_setCustomVar', 5, 'Fasterize', 'untracked', 2]);
}

_gaq.push(['_setSiteSpeedSampleRate', 100]);

// Fin du code à copier-coller

_gaq.push(['_trackPageview']);

(function() {
  var ga = document.createElement('script');
  ga.type = 'text/javascript';
  ga.async = true;
  ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
  (document.getElementsByTagName('head')[0] || document.getElementsByTagName('body')[0]).appendChild(ga);
})();