When a page trigger layout during scroll events and with scroll snap, dragging the scrollbar on a Mac causes a lot of jitter while scrolling. The issue is that during layout the code is trying to snap. Each new movement of the scroll bar unsnaps briefly and then the relayout snaps again.
Created attachment 432460 [details]
Created attachment 432678 [details]
Created attachment 432774 [details]
Created attachment 432874 [details]
Committed r279564 (239395@main): <https://commits.webkit.org/239395@main>
All reviewed patches have been landed. Closing bug and clearing flags on attachment 432874 [details].