The material is used. It needs to be one of the new semantic materials to work in dark mode.
<rdar://problem/39135535>
Created attachment 342047 [details] Patch
Created attachment 342048 [details] Patch
Comment on attachment 342048 [details] Patch Clearing flags on attachment: 342048 Committed r232546: <https://trac.webkit.org/changeset/232546>
All reviewed patches have been landed. Closing bug.