Consider dropping initServiceWorkerMessageEvent()

[bashi]

ServiceWorkerMessageEvent has initServiceWorkerMessageEvent() [1], but I think we should drop this method because as the note[2] says, initEvent() method only exists for historical reason and we can use constructor to initialize events.

[1] https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#serviceworkermessage-event-initserviceworkermessageevent-method
[2] https://dom.spec.whatwg.org/#dom-event-initeventtype-bubbles-cancelable

[jungkees]

Agreed. @jakearchibald @annevk Can there be any concern about dropping this method considering devs historically having used the initMessageEvent()? (Although they're now defined as unrelated interfaces.)

[domenic]

+1, new events should not have this

[jungkees]

Thanks!