REGRESSION (r290628): Scrubber makes a visual trail when scrubbing on tv.youtube.com
Created attachment 455025 [details] Patch
<rdar://problem/90310316>
<rdar://problem/90451319>
Created attachment 455034 [details] Patch
Committed r291493 (248605@main): <https://commits.webkit.org/248605@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 455034 [details].