[css-grid-1][masonry] Replaced content items should stretch by default.

[fantasai]

In #9041 (comment) @bfgeek suggests that in Masonry layout, replaced elements should stretch by default (like non-replaced elements) rather than remaining start-aligned.

(Fwiw, I'm not convinced that there's a reason for Masonry and Grid to diverge here.)

[tabatkins]

The reason to diverge is that I don't think I've ever seen a masonry layout with images in the wild that didn't stretch the images to fill the track. It would look pretty weird/bad for the track to have a "ragged edge" from start-aligned images by default.

[fantasai]

@tabatkins Images don't stretch by default anywhere else in CSS though, so it would be pretty inconsistent.

(Also, most of those you've seen in the wild were probably images inside non-replaced elements that stretched.)

[bfgeek]

They stretch in flexbox.