Integrate requestIdleCallback with HTML5 event loop.
Pull request: https://github.com/WebKit/WebKit/pull/16417
Committed 266622@main (03c76b1a950a): <https://commits.webkit.org/266622@main> Reviewed commits have been landed. Closing PR #16417 and removing active labels.
<rdar://problem/113459096>
Re-opened since this is blocked by bug 259875
Pull request: https://github.com/WebKit/WebKit/pull/16474
Committed 266687@main (f7971be8f91b): <https://commits.webkit.org/266687@main> Reviewed commits have been landed. Closing PR #16474 and removing active labels.