Since we check against an instance method, we should use instancesRespondToSelector.
<rdar://problem/101812900>
Pull request: https://github.com/WebKit/WebKit/pull/6008
Committed 256200@main (60e1fb82eaf0): <https://commits.webkit.org/256200@main> Reviewed commits have been landed. Closing PR #6008 and removing active labels.