VRDisplayEvent implementation

[ygilquin-gpsw]

VRDisplayEvent received when onvrdisplaypresentchange is triggered should have a display property pointing on the VRDisplay instance.

From the spec

interface VRDisplayEvent : Event {
  readonly attribute VRDisplay display;
  readonly attribute VRDisplayEventReason? reason;
};

This would be a great addition. Thanks.

[spite]

Should be fixed with this 4655fdf but I don't see an easy way to properly mimick VRDisplayEvent with CustomEvents. I hope nobody tries to check the event typeof...