(regression) iframe: hovering the iframe doesn't un-hover parent document nodes

[paulrouget]

Previous issue: #7865

Hovering the div then moving mouse hover the iframe doesn't uncover the div.

<style>

  div {
    width: 100%;
    height: 20px;
    background: red;
  }
  div:hover {
    background: blue;
  }
  iframe {
    display: block;
    width: 100%;
    height: 100px;
    background: green;
    border-width: 0;
  }
</style>

<div></div>
<iframe src="http://example.com"></iframe>

[paulrouget]

We don't send the mousemove event to the previously hovered pipeline when using webrender.

See:

servo/components/compositing/compositor.rs

Line 1468 in 7d978e7

match self.find_topmost_layer_at_point(cursor / self.scene.scale) {

[nox]

I can still reproduce this.