USBConnectionEvent needs a constructor

[foolip]

http://wicg.github.io/webusb/#events

It has a constructor in Chromium:
https://chromium.googlesource.com/chromium/src/+/2fe96ea775a73ad5dcc05105f57be096d302baa2/third_party/WebKit/Source/modules/webusb/USBConnectionEvent.idl

But unless device is made nullable, some tweaks are needed to ensure that it's never null, a non-optional dict with a required member:

[Constructor(DOMString type, USBConnectionEventInit eventInitDict)]
interface USBConnectionEventB : Event {
    [SameObject] readonly attribute USBDevice device;
};

dictionary USBConnectionEventInit : EventInit {
    required USBDevice device;
};

[foolip]

Great, thank you!