Store fewer raw pointers in containers in GridTrackSizingAlgorithm.
Pull request: https://github.com/WebKit/WebKit/pull/17785
Committed 268021@main (b68d76a2de1c): <https://commits.webkit.org/268021@main> Reviewed commits have been landed. Closing PR #17785 and removing active labels.
<rdar://problem/115556083>