Have ScrollingMomentumCalculator work in terms of ScrollExtents
Created attachment 438603 [details] Patch
Created attachment 438628 [details] Patch
Created attachment 438632 [details] Patch
Committed r282749 (241886@main): <https://commits.webkit.org/241886@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 438632 [details].
<rdar://problem/83308466>