Migrate protobuf to google.golang.org.

[junghao]

Hi,

I'd like to know if there's any plan in migrating the usage of github.com/golang/protobuf to google.golang.org/protobuf ?

[bcmills]

github.com/golang/protobuf is now implemented in terms of google.golang.org/protobuf, so as far as I know there is no pressing need to migrate.

The github.com/golang/groupcache package certainly cannot be migrated, since that would be a breaking change (and would in turn cause a breaking change in the groupcache.ProtoGetter interface).

[benjsmi]

Just an outside observer here but github.com/golang/protobuf is deprecated.