When dragging media controls in fullscreen on macOS, there is a lot of flickering for the backdrop, and sometimes the rendered content of the controls disappear.
<rdar://problem/30687803>
Created attachment 305083 [details] Patch
Comment on attachment 305083 [details] Patch Clearing flags on attachment: 305083 Committed r214258: <http://trac.webkit.org/changeset/214258>
All reviewed patches have been landed. Closing bug.