For playbin2 case we have some code to keep track of sticky tag events in TrackPrivateBase. For playbin3 case we can simply monitor the tags property on the GstStream.
Pull request: https://github.com/WebKit/WebKit/pull/6394
Committed 256649@main (d6ad2e4228d0): <https://commits.webkit.org/256649@main> Reviewed commits have been landed. Closing PR #6394 and removing active labels.
<rdar://problem/102316262>