Simplify / Optimize Element::insertedIntoAncestor() a bit, similarly to what was done for Element::removedIntoAncestor() in 253924@main.
Pull request: https://github.com/WebKit/WebKit/pull/3821
Committed 253965@main (31257419593c): <https://commits.webkit.org/253965@main> Reviewed commits have been landed. Closing PR #3821 and removing active labels.
<rdar://problem/99356667>