IPC::Connection message throttling refers to main runloop This makes it a bit hard to make Connection runloop agnostic
<rdar://problem/100974660>
Pull request: https://github.com/WebKit/WebKit/pull/5190
Committed 255579@main (50386bbd03a7): <https://commits.webkit.org/255579@main> Reviewed commits have been landed. Closing PR #5190 and removing active labels.