Basically, make an WebKit internal implementation of the following that can be used with run-webkit-tests: https://github.com/w3c/webdriver/pull/1695
<rdar://problem/102399664>
Pull request: https://github.com/WebKit/WebKit/pull/6539
Committed 256916@main (438bd44b426e): <https://commits.webkit.org/256916@main> Reviewed commits have been landed. Closing PR #6539 and removing active labels.