This is in preparation for having proper inline boxes on the line.
Created attachment 405140 [details] Patch
<rdar://problem/66378814>
Created attachment 407072 [details] Patch
Created attachment 407074 [details] Patch
Committed r266048: <https://trac.webkit.org/changeset/266048> All reviewed patches have been landed. Closing bug and clearing flags on attachment 407074 [details].