LineBuilder just builds the line, no need for LineBox.
Created attachment 405765 [details] Patch
<rdar://problem/66709575>
Created attachment 407390 [details] Patch
Created attachment 407392 [details] Patch
Committed r266231: <https://trac.webkit.org/changeset/266231> All reviewed patches have been landed. Closing bug and clearing flags on attachment 407392 [details].