adoptNode() needs to account for <iframe> and friends #1428
Description
What is the issue with the DOM Standard?
In particular, if you run adoptNode() on an iframe with the iframe's nested document as this, all browsers throw.
I don't think we can really use the "adopting steps" for this as they run too late and it also seems like it's specific to adoptNode() and not adopt in general. I'm not entirely sure why it happens as the iframe element could certainly be removed and all would be fine I think, but that's just not the reality.