Support for Service Worker Life Cycle Events

[NoelAbrahams]

Hi

Support for events notifying changes to the state of a Service Worker is not consistent across browsers, eg chakra-core/ChakraCore#5815

Please consider adding support for the following:

• onupdatefound
• waiting
• installing
• active

The last two appear to be supported across browsers, but not the first two.

Thanks!

[NoelAbrahams]

Not sure if this is too granular but ServiceWorkerRegistration.update is also part of the life cycle.