UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3012.0 Safari/537.36

Steps to reproduce the problem:
1. Visit this demo page: https://www.scirra.com/labs/bugs/slow-hittest-perf/
2. Open dev tools, go to Performance tab
3. Start recording a profile
4. Focus the demo page and just move the mouse in circles a few times
5. End profile and inspect results

What is the expected behavior?
Minimal activity in performance tab. This should not be a high-CPU activity.

What went wrong?
Performance tab indicates back-to-back "Hit Test" tasks on main thread, each taking ~8ms on a high-end desktop. Windows task manager also indicates one core maxing out CPU usage while the mouse is moving.

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 58.0.3012.0  Channel: canary
OS Version: 10.0
Flash Version: Shockwave Flash 25.0 r0

Edge and Firefox do not appear to be affected. Their performance timelines are more or less empty for doing the same thing. I don't know if they actually list "hit test", but Windows task manager shows CPU usage is still 0-1% while moving the mouse in those browsers, vs. ~12% (on 8 thread system, i.e. one core maxed) in Chrome.

We have a production web app where "Hit test" occupies so much main thread time it impacts scrolling performance.