This is in preparation for adding vertical alignment support.
<rdar://problem/51482708>
Created attachment 371496 [details] Patch
Created attachment 371504 [details] Patch
Comment on attachment 371504 [details] Patch Clearing flags on attachment: 371504 Committed r246158: <https://trac.webkit.org/changeset/246158>
All reviewed patches have been landed. Closing bug.