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

[paulrouget]

In this example, hovering the div turns it blue. Then moving the cursor to the iframe without leaving the div won't turn it back to red.

<style>
  div {
    width: 100px;
    height: 100px;
    background: red;
  }

  div:hover {
    background: blue;
  }

  iframe {
    margin: 10px;
    width: 600px;
    height: 300px;
    border-width: 0;
  }
</style>

<div></div>

<iframe mozbrowser remote src='http://google.com'></iframe>

[jdm]

I'm pretty sure this is due to the new mouse move event being sent to the iframe's script task, rather than the parent's so the code in Document::handle_mouse_move_event never sees the list of currently-hovered elements that require checking. We might need to store the pipeline id that received the last mouse move event in the constellation/compositor and ensure that we send a mouse move event to that as well if it's different than the current one.

[paulrouget]

@jdm are you still looking at this? Does that depend on @mrobinson work?

[jdm]

I forgot about this and haven't done any investigation beyond the original comment.