<!DOCTYPE HTML>
<title>Don't crash when mutating style attribute with non-initial transition</title>
<link rel="help" href="https://crbug.com/1313554">
<style>
  #foo { transition: --unset 1s linear; }
</style>
<div id=foo style="background-color:red">PASS if no crash</div>
<script>
foo.offsetTop;
foo.style.backgroundColor = 'green';
foo.offsetTop;
</script>
