This patch is a combination of a follow-up of https://github.com/WebKit/WebKit/pull/3746, and a fix for a race condition I independently discovered before said PR was published. Minor cleanups for pr/3746 are done, additional logging is added, MediaPlayerPrivateGStreamer::m_abortableTaskQueue is renamed to MediaPlayerPrivateGStreamer::m_sinkTaskQueue, comments are added, and most importantly: the task queue is flushed when a GStreamer flush is received. This fixes a race condition on MSE flushes.
Pull request: https://github.com/WebKit/WebKit/pull/3802
Committed 254142@main (e55d1903cf10): <https://commits.webkit.org/254142@main> Reviewed commits have been landed. Closing PR #3802 and removing active labels.