ServiceWorker

5059261f - Check for Run Service Worker failure and disallow starting redundant workers. (#1419)

Check for Run Service Worker failure and disallow starting redundant workers. (#1419) This cleans up Run Service Worker to block until the worker is running or fails to start. Callsites are updated to check if the worker is running before proceeding. It also disallows starting a redundant worker. postMessage is dropped silently if starting the service worker failed. Addresses #1146 and #1403.