We add a skeleton code for experimental ManagedMediaSource and ManagedSourceBuffer objects.
<rdar://problem/105206629>
Pull request: https://github.com/WebKit/WebKit/pull/9848
Committed 260106@main (3d03d36204f5): <https://commits.webkit.org/260106@main> Reviewed commits have been landed. Closing PR #9848 and removing active labels.