Make plug-in loading fully async instead of during post style resolution callbacks.
Created attachment 460923 [details] WIP
Pull request: https://github.com/WebKit/WebKit/pull/2421
Pull request: https://github.com/WebKit/WebKit/pull/2461
Committed 252541@main (f4b10fa093ec): <https://commits.webkit.org/252541@main> Reviewed commits have been landed. Closing PR #2461 and removing active labels.
<rdar://problem/97129714>