What is the "Deferred long-running timer tasks" warning in the Chrome DevTools?

i was inspect with my page and i get this warning...

Deferred long-running timer task(s) to improve scrolling smoothness. See crbug.com/574343

I've also seen:

Blink deferred a task in order to make scrolling smoother. Your timer tasks should take less than 50ms to run to avoid this. Please see https://developers.google.com/web/tools/chrome-devtools/profile/evaluate-performance/rail and https://crbug.com/574343#c40 for more information.

What is this?