Re: [w3c/ServiceWorker] Clarification on what happens during a terminated activation (#1372)

> What if Chrome's service worker process/thread crashes during activation, due to something outside the control of the JavaScript code being executed during the activate handler(s)?

Good question! Chrome's algorithm is roughly:
1) Browser asks the renderer to dispatch the activate event handler to the service worker.
2) Browser waits for the renderer to report back that event handler finished. This includes detecting that the renderer died or the worker thread died, if the connection is gone the browser knows the event is done. Also the timeout mechanism can forcefully abort the event handler and declare it finished.
3) Once it finished, the browser writes "activated" to disk.

As an exception in step 3 if the browser detects it's shutting down, it doesn't write "activated" to disk and will retry the next time the worker is used in some browser session.

This mostly matches the spec, except the spec doesn't account for crashing/shutdown between dispatching the activate event and running Update Worker State to activated in https://w3c.github.io/ServiceWorker/#activation-algorithm.

I'd like to change Chrome to remove the shutdown exception and instead only run the activate event if we're not in shutdown already. I could shuffle where we write "activated" to disk but either way there can be an edge case due to this cross-process model. If the browser process writes "activated"  once it asks the renderer to dispatch the event, then a browser crash/shutdown occurs, the worker can become "activated" without activate ever firing from the POV of the developer. If the browser process writes "activated" after the event finishes, and a browser crash/shutdown occurs before that, the worker can get an activate event again in the next browser session.

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