We'll need a tile layer per PDF page for future off-main-thread drawing.
<rdar://problem/122399196>
Pull request: https://github.com/WebKit/WebKit/pull/23931
Committed 274342@main (dbb83825aeb7): <https://commits.webkit.org/274342@main> Reviewed commits have been landed. Closing PR #23931 and removing active labels.