[macOS] Scrolling synchronization part 2: Have the scrolling thread detect when the main thread is slow to respond to start a rendering update
Created attachment 399908 [details] Patch
Committed r261999: <https://trac.webkit.org/changeset/261999> All reviewed patches have been landed. Closing bug and clearing flags on attachment 399908 [details].
<rdar://problem/63494553>