Reduced use of CheckedRef for non-stack variables in Source/WebKit/UIProcess.
Pull request: https://github.com/WebKit/WebKit/pull/22674
Committed 272952@main (a54bc150e710): <https://commits.webkit.org/272952@main> Reviewed commits have been landed. Closing PR #22674 and removing active labels.
<rdar://problem/120881402>