Have RenderObject subclass CanMakeCheckedPtr so that we can adopt CheckedPtr / CheckedRef in rendering code for safety. We were previously relying on WeakPtr but it turned out to be too costly and cause performance regressions.
Pull request: https://github.com/WebKit/WebKit/pull/18036
Committed 268298@main (60da0af82782): <https://commits.webkit.org/268298@main> Reviewed commits have been landed. Closing PR #18036 and removing active labels.
<rdar://problem/115874373>