/usr/share/gocode/src/code.google.com/p/goprotobuf is in golang-goprotobuf-dev 0.0~git20170808.0.1909bc2-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/gocode/src/code.google.com/p/../../github.com/golang/protobuf