[ServiceWorker] consider exposing install time on ServiceWorker DOM object (#842)

It might be nice to expose when a service worker was installed.  This could be used for debugging and other diagnostics.  For example, the site could send the value to the server and if it sees that a client is not updating for some reason then send the serviceworker kill header.

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/842