Right now, each IdleCallbackController has a notion of idle period. Move this to WindowEventLoop so that multiple IdleCallbackControllers in multiple documents can share the same deadline if they also share WindowEventLoop.
Pull request: https://github.com/WebKit/WebKit/pull/16426
Committed 266745@main (b7bc61d59e5e): <https://commits.webkit.org/266745@main> Reviewed commits have been landed. Closing PR #16426 and removing active labels.
<rdar://problem/113655590>