See HTMLMediaElement::buffering() and HTMLMediaElement::stalled(), we need to use PseudoClassChangeInvalidation every time one of the conditions change.
<rdar://problem/103438119>
Pull request: https://github.com/WebKit/WebKit/pull/8606
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/37924
Committed 258891@main (2974b49cf64d): <https://commits.webkit.org/258891@main> Reviewed commits have been landed. Closing PR #8606 and removing active labels.