We need to add copy for CSSCounterStyleRule since a change on style will force a copy-on-write operation.
<rdar://problem/109082260>
Pull request: https://github.com/WebKit/WebKit/pull/13638
Committed 263870@main (37bb9afc0b47): <https://commits.webkit.org/263870@main> Reviewed commits have been landed. Closing PR #13638 and removing active labels.