<%= session[:referer] %> 부분에 레퍼러 들어가면 됨.

gistfile1.txt

<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', '<%= Rails.application.secrets.ga_tracking_id%>', '<%= Rails.application.secrets.url %>');
ga('set', 'referrer', '<%= session[:referer] %>');
ga('send', 'pageview');
</script>