Add missing hyphens to 'webkit's in <width-or-height-keyword> grammar
<rdar://problem/102682234>
Pull request: https://github.com/WebKit/WebKit/pull/6826
Committed 257038@main (3a25c2011c31): <https://commits.webkit.org/257038@main> Reviewed commits have been landed. Closing PR #6826 and removing active labels.