We have a few different areas in the code where we traverse up an ancestor subgrid chain. We should add an iterator that performs this logic
<rdar://problem/117083828>
Pull request: https://github.com/WebKit/WebKit/pull/19177
Committed 269443@main (dfe2536d7273): <https://commits.webkit.org/269443@main> Reviewed commits have been landed. Closing PR #19177 and removing active labels.