Only show GA content experiment to mobile traffic

mobile-experiment.html

<script>
    ////// START EDITING HERE
var utmx_key = 'XXXXXXX-X', // change this to your experiment key
    show_on = 'mobile',     // Can be 'mobile' or 'desktop'
    ///// STOP EDITING HERE
    ///////////////////////////
    
    is_mobile = function () {
        return /android|webos|iphone|ipad|ipod|blackberry|iemobile|opera\s?mini/i.test(navigator.userAgent.toLowerCase());
    },
    show_experiment = function() {
        return (show_on === 'mobile' && is_mobile()) || (show_on === 'desktop' && !is_mobile());
    },

    utmx_section = function() { },
    utmx = function() { };

if ( show_experiment() ) {

  // <!-- Google Analytics Content Experiment code -->
  function utmx_section(){}function utmx(){}(function(){var
  k=utmx_key,d=document,l=d.location,c=d.cookie;
  if(l.search.indexOf('utm_expid='+k)>0)return;
  function f(n){if(c){var i=c.indexOf(n+'=');if(i>-1){var j=c.
  indexOf(';',i);return escape(c.substring(i+n.length+1,j<0?c.
  length:j))}}}var x=f('__utmx'),xx=f('__utmxx'),h=l.hash;d.write(
  '<sc'+'ript src="'+'http'+(l.protocol=='https:'?'s://ssl':
  '://www')+'.google-analytics.com/ga_exp.js?'+'utmxkey='+k+
  '&utmx='+(x?x:'')+'&utmxx='+(xx?xx:'')+'&utmxtime='+new Date().
  valueOf()+(h?'&utmxhash='+escape(h.substr(1)):'')+
  '" type="text/javascript" charset="utf-8"><\/sc'+'ript>')})();

}
</script><script>utmx('url','A/B');</script>
<!-- End of Google Analytics Content Experiment code -->