Further simplify the class hierarchy.
Created attachment 462770 [details] Patch
Commit message contains (OOPS!), blocking PR #None
<rdar://problem/100754684>
Created attachment 462785 [details] Patch for landing
Committed 255120@main (5472d07a1e1d): <https://commits.webkit.org/255120@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 462785 [details].