With the old API we just use a 0 seconds timer, but with the new API we can use the buffer-renderer signal of WPEView to actually call the callback after the next buffer is rendered. This will hopefully reduce the flakiness of ref tests.
Pull request: https://github.com/WebKit/WebKit/pull/24405
Committed 274710@main (1512e48affb3): <https://commits.webkit.org/274710@main> Reviewed commits have been landed. Closing PR #24405 and removing active labels.