[ServiceWorker] Add note that activate event cannot fail SW activation (#776)

Currently the activate algorithm reports exceptions from the activate event handler, but still allows activation to complete.  In addition, it allows the activate event handler to be killed due to timeout with the SW still activating.

I see that this was intentional due to issue #447.

It would be nice, though, to add a note to the spec that this is intentional.  The reasoning behind this behavior is not immediately obvious when reading the spec.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/776