Unexpected focus-within behaviour when layout is forced during blur event

[Bastien Caudan]

On a case where an element visibility is conditioned by a :focus-within pseudo class:

<style>
  .dropdown .dropdown-content {
    visibility: hidden;
  }
  .dropdown:focus-within .dropdown-content {
    visibility: visible;
  }
</style>
<div class="dropdown">
  <label tabindex="0">Click</label>
  <ul tabindex="0" class="dropdown-content">
    <li><a href="#foo">Go to foo</a></li>
    <li><a href="#bar">Go to bar</a></li>
  </ul>
</div>

When switching the focus to an inner element (clicking on one of the links) with a forced layout during the blur event, the inner element is not focused. 
Without the forced layout on the blur event it behaves as expected.

I have setup a reproduction case here: https://codesandbox.io/s/stupefied-andras-p79o0x?file=/index.html
Other browsers seem to handle this case without issue.

[Radar WebKit Bug Importer]

<rdar://problem/105118742>