On your example pages (as well as my own experiments), I'm seeing a full document layout in Chrome:

It's only taking around 0.5ms, but I still find it strange that rstats is forcing the entire document to relayout. And in terms of a single frame, that's almost 3% of the total time allotted for 60fps. Obviously rendering rstats is not free, but it should ideally use as little time as possible.
Thanks for making rstats, it's been really cool to use!