Re: [ServiceWorker] A worker that fails to activate should relinquish its controllees (#659)

Re https://github.com/slightlyoff/ServiceWorker/issues/659#issuecomment-87778808, here's some investigation about what we do with a registration. (http://slightlyoff.github.io/ServiceWorker/spec/service_worker/sw-registration-figure.svg.)

**[Create Registration]** A registration is created only by `navigator.serviceWorker.register()`.

**[Update Registration]** The state of the registration can be mutated by:
  - `navigator.serviceWorker.register()`
  - `registration.update()`
  - Soft Update (This can be called by UA internal context and other APIs such as Push API.)

**[Delete Registration]** The registration can be deleted by:
  - `registration.unregister()`
  - Handle Service Worker Client Unload (when there's no other client left and the uninstalling flag is set.)
  - **Errors in Update**
  - **Errors in Install**

The first two points in **[Delete Registration]** are explicit, so we may want to check the rest of the points. Here's **the list of errors triggering Clear Registration from Update**:
  - Request constructor (to prepare fetching script) throws
  - Network error by detecting a redirect
  - Script's MIME type mismatch
  - `Service-Worker-Allowed` header parsing failure
  - Script's location violation
  - An uncaught runtime script error when run a worker with the fetched script

**The list of errors triggering Clear Registration from Install**:
  - An uncaught runtime error in the oninstall event listener
  - Install failure detected by the rejection of waitUntil promise

IMO, these errors are mostly something devs need to fix during the development/deployment. (Those can be fixed by the next Update attempt.) In the case of the registration which should be permanently removed, an explicit call to `registration.unregister()` seems reasonable. Also as @jakearchibald pointed out, the registration through the corresponding ServiceWorkerRegistration object is bound to PushManager, SyncManager, GeofenceManager, etc.

Are there other concerns that I missed?

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