focus / blur events aren't dispatched on `window` and `document` objects

[Gozala]

Here is an example to reproduce it:

https://output.jsbin.com/picawu/3

This is either regression since focus / blur used to be dispatched on the document, or it could be that @paulrouget had a patch for this that did not end up in upstream.

P.S.: Webkit dispatches focus / blur only on window while gecko dispatches them on both window and document.

[jdm]

@Gozala When do you expect these to be fired for browser.html?

[Gozala]

@Gozala When do you expect these to be fired for browser.html?

I expect blur events to be dispatched when servo window looses a focus (say you switch to your editor window), then if you switch back to servo window I'd expect focus event should be dispatched.

[jdm]

This sounds like #9482, in that case.