Follow-up to Bug 265381 There are no grid tracks in the masonry axis of a masonry layout (i.e.: no rows when the masonry direction is vertical, vice-versa for horizontal). It may still be useful to outline the individual grid items and represent the grid gap between them.
<rdar://problem/118833939>
https://github.com/WebKit/WebKit/pull/22941 exposed the necessary metrics to implement the drawing of outlines around grid items.
https://bugs.webkit.org/show_bug.cgi?id=267736