analytics tracking in chrome extension

ext.js

var _gaq = _gaq || [];
_gaq['_setAccount'] =  'UA-XXXXX-1';
_gaq['_setDomain'] = 'youdomain.com';

function rand(from,to)
{
    return Math.floor(Math.random()*(to-from+1)+from);
}

var i     = 1000000000,
utmn      = rand(i,9999999999), //random request number
cookie    = rand(10000000,99999999), //random cookie number
random    = rand(i,2147483647), //number under 2147483647
today     = new Date().getTime(),
win       = window.location,
urchinUrl = window.location.protocol+'//www.google-analytics.com/__utm.gif?utmwv=1.3&utmn='
    +utmn+'&utmsr=-&utmsc=-&utmul=-&utmje=0&utmfl=-&utmdt=-&utmhn='
    +_gaq._setDomain+'&utmr='+win+'&utmp='
    +'/'+document.location.href+'&utmac='
    +_gaq._setAccount+'&utmcc=__utma%3D'
    +cookie+'.'+random+'.'+today+'.'+today+'.'
    +today+'.2%3B%2B__utmb%3D'
    +cookie+'%3B%2B__utmc%3D'
    +cookie+'%3B%2B__utmz%3D'
    +cookie+'.'+today
    +'.2.2.utmccn%3D(referral)%7Cutmcsr%3D' + win.host + '%7Cutmcct%3D' + win.pathname + '%7Cutmcmd%3Dreferral%3B%2B__utmv%3D'
    +cookie+'.-%3B';


var img = document.createElement('img');
    img.src = urchinUrl;
    img.onload = function(){
      document.getElementsByTagName('body')[0].removeChild(this);
    }
    document.getElementsByTagName('body')[0].appendChild(img);