User agent/referrer check

gistfile1.html

<script>
  (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
  (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
  m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
  })(window,document,'script','//www.google-analytics.com/analytics.js','ga');

  ga('create', 'XX-XXXXXXX-XX', 'auto');

  if (/\/FBIOS;/.test(navigator.userAgent) === true) {
    ga('set', 'referrer', 'http://www.facebook.com/__ios_webview__');
  } else if (/\/FB4A;/.test(navigator.userAgent) === true) {
    ga('set', 'referrer', 'http://www.facebook.com/__android_webview__');
  }

  ga('send', 'pageview');

</script>