ENABLE_MANAGED_MEDIA_SOURCE isn't set on GTK & Co and cmake based build.
<rdar://problem/105540966>
Pull request: https://github.com/WebKit/WebKit/pull/10214
Committed 260671@main (86c12d6b8e31): <https://commits.webkit.org/260671@main> Reviewed commits have been landed. Closing PR #10214 and removing active labels.