This test uses CSS function -webkit-image-set (image-set is not implemented in Gecko).

I searched for other tests that have image-set and there are a few:
https://searchfox.org/mozilla-central/search?q=image-set&path=testing%2Fweb-platform%2Ftests

we have css/css-images/image-set/* tests:
https://searchfox.org/mozilla-central/source/testing/web-platform/tests/css/css-images/image-set

these 2 tests are marked as perma fail, which would make sense.

I see paint-timing/fcp-only/fcp-bg-image-set.html as having image-set, and it is marked as perma fail.

For tests that depend on features we don't support, I am marking them as backlog so they run daily but not normally on try or on autoland.

I would like to know if I should mark the 4 tests (2 css, 1 fcp, 1 service-worker) as backlog, or just the test in the title.

ni on :perry as I saw in another but that :ytausky was afk for a bit.

I implemented image-set and this test works now.