WebVTT regions are not positioned according to the spec
<rdar://problem/23091897>
Pull request: https://github.com/WebKit/WebKit/pull/16848
*** Bug 260410 has been marked as a duplicate of this bug. ***
Committed 268787@main (eae66f440e60): <https://commits.webkit.org/268787@main> Reviewed commits have been landed. Closing PR #16848 and removing active labels.