We introduced a regression in https://bugs.webkit.org/show_bug.cgi?id=167935 where the volume slider is initially empty until we interact with it once.
<rdar://problem/31319077>
Created attachment 305726 [details] Patch
Comment on attachment 305726 [details] Patch Clearing flags on attachment: 305726 Committed r214540: <http://trac.webkit.org/changeset/214540>
All reviewed patches have been landed. Closing bug.