Why the CompanionWindow interface?

[domenic]

[SecureContext, Exposed=Window]
interface CompanionWindow {
  attribute DOMString name;
  void close();

  readonly attribute WindowProxy? contentWindow;
};

This seems to duplicate name and close() from WindowProxy. Why not just expose the WindowProxy directly?

Overall, I'd like to see some discussion of exactly how much communication to/manipulation of the companion windows we want to expose, and for what use cases. Given what a mess cross-window communication is in general, starting from a base of zero (or maybe a base of postMessage() + close()) would be nicer.