Make sure the ProcessAssertion gets destroyed on the main thread.
<rdar://81048308>
Created attachment 434208 [details] Patch
Comment on attachment 434208 [details] Patch r=me
Committed r280299 (239952@main): <https://commits.webkit.org/239952@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 434208 [details].