Subscriber implements Service interface

[piotrpolatowski]

Why new Subscriber implementation is a decorator for AbstractService and not implement Service interface directly?

It makes it harder to use with com.google.common.util.concurrent.ServiceManager

[garrettjonesgoogle]

Because we don't want to expose Guava on our surface. We want to be able to create a variant of google-cloud-java with Guava shaded for those who are using older versions of Guava that aren't compatible with our version.

[garrettjonesgoogle]

I'm going to close this out now. Re-open if you have more concerns.