Use a WeakHashSet to store MediaStreamPrivate observers
Created attachment 396413 [details] Patch
Created attachment 396958 [details] Patch
Created attachment 396959 [details] Patch
Committed r260379: <https://trac.webkit.org/changeset/260379> All reviewed patches have been landed. Closing bug and clearing flags on attachment 396959 [details].
<rdar://problem/62066856>