chromium/third_party/blink/web_tests/fast/hidpi/image-set-fallback-expected.html

<!DOCTYPE html>
<script src="resources/srcset-helper.js"></script>
<style>
  .foo {
    width: 100px;
    height: 100px;
    content: url('resources/red-100-px-square.png');
  }
</style>

<div>
  This test passes if the div below is a 100px red square.
</div>
<br>
<div class="foo"></div>