What version of gRPC are you using?

v1.21.0

What did you expect to see?

Prior to 745aa0a, the //compiler:grpc_java_plugin target was publicly visible for use by external bazel workspaces. This allowed use of the protoc plugin in Bazel workspaces that use grpc-java as a dependency, in particular the rules_proto rules. Since this commit, it it no longer possible.

Is there a particular motivation for marking it as non-public?