Fix and incident report for most popular JS errors

This refactor of the inline most popular A/B test to fix the JS errors seen in production today. I have also written up an incident report to detail the issues and action points needed.

Big fail on my behalf for rushing and not testing properly. :frowning: 

![Fail](http://www.funlyest.com/files/articles/460/1370146795.gif.pagespeed.ce.Atk2tHOqOa.gif)