Add support for the contains value for line grid snapping, so that it is possible to center headers etc. in between grid lines.
Created attachment 126097 [details]
Comment on attachment 126097 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=126097&action=review
> + LayoutUnit result = delta;
This can go back down to line 400 where it was before this patch.