iframes not clipped by border radius

[paulrouget]

Affects browserhtml

border-radius on a iframe and its parents doesn't clip the content of the iframe.

Happens both with and without webrender.

<style>
  div {
    display: inline-block;
    border-radius: 0 0 50px 50px;
    border: 5px solid red;
    overflow: hidden;
  }
  iframe {
    border: 5px solid green;
    display: block;
    height: 100px;
    width: 100px;
    border-radius: 50px 50px 0 0;
  }
</style>
<div>
  <iframe src="data:text/html,<style>body{background:orange}</style>"></iframe>
</div>

[pcwalton]

We actually don't support clipping iframes at all. The appropriate clip region isn't being communicated to WebRender, and WebRender isn't using it. Working on a fix.

[mrobinson]

Assigning myself here as well, because I've been working on this as well and should be able to have a fix rather quickly.

[mrobinson]

This should be fixed by #17771.