After r269593, mach-lookup to the service 'com.apple.audio.SystemSoundServer-OSX' in the WebContent process can be denied.
<rdar://problem/69019399>
Created attachment 415537 [details] Patch
Created attachment 415545 [details] Patch
Comment on attachment 415545 [details] Patch r=me. Windows failure cannot be related, since it does not use the sandbox and none of this code (or testing) executes on Windows.
Committed r270517: <https://trac.webkit.org/changeset/270517> All reviewed patches have been landed. Closing bug and clearing flags on attachment 415545 [details].
Thanks for reviewing!