Make sure the Frame always gets destroyed on the main thread. Since http://trac.webkit.org/changeset/181791, Frame is ThreadSafeRefCounted and captured on other threads. We should make sure the Frame is always destroyed on the main thread though, since it is a main thread object and we hold WeakPtrs to it in many places.
<rdar://75131946>
Created attachment 425220 [details] Patch
Committed r275475: <https://commits.webkit.org/r275475> All reviewed patches have been landed. Closing bug and clearing flags on attachment 425220 [details].