Banzai::Filter::SyntaxHighlightFilter is slow
This filter is used for rendering syntax highlighted blocks of code. As per http://performance.gitlab.net/dashboard/db/markdown-filter-methods?var-process_type=rails&var-method=Banzai%3A%3AFilter%3A%3ASyntaxHighlightFilter%23call this filter can take between 140 ms and 840 ms. Most likely most of the time is spent in Rouge since the filter itself doesn't do a whole lot. As a start we should instrument Rouge so we can figure out if it's our own code or Rouge.