Add support for ContentVisibilityAutoStateChangeEvent.
Created attachment 466933 [details] Initial patch
<rdar://problem/112135100>
Pull request: https://github.com/WebKit/WebKit/pull/15926
Committed 267340@main (5b575ff841de): <https://commits.webkit.org/267340@main> Reviewed commits have been landed. Closing PR #15926 and removing active labels.