Drop unnecessary downcast<>() calls in InputType::isValidValue(), for performance reasons.
<rdar://problem/123953564>
Pull request: https://github.com/WebKit/WebKit/pull/25377
Committed 275599@main (98f0251a08ba): <https://commits.webkit.org/275599@main> Reviewed commits have been landed. Closing PR #25377 and removing active labels.