Re: [ServiceWorker] Clients & postMessage (#609)

Spec'ed `ServiceWorker.postMessage()` and `Client.postMessage()`: 6dfce0aacceeef41c813c4680c7f67b96f80c4b6. Just done it in Friday evening and may need to continue the work next week. ;-)

Notes:
  - Now `ServiceWorker` interface is derived from `EventTarget`. (It still implements `AbstractWorker`.) So, the unused `terminate()` method is gone. Implementers: please give me feedback if you have concern about this change.
  - `postMessage` for both directions is specified not by means of `MessagePort` but by queuing a task to the `ServiceWorkerContainer/ServiceWorkerGlobalScope` object directly. 

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/609#issuecomment-76386122