Updating the jar binary

1. Go to http://search.maven.org/
2. Search for g:“com.google.protobuf”
3. Download the “jar” link from protobuf-java and put them in <Bazel tree>/third_party/protobuf/<version>

Updating protobuf.bzl and the src/ directory:

1. git clone http://github.com/google/protobuf.git
2. git checkout <tag or commithash> (e.g. v3.0.0 or e8ae137)
3. mkdir -p third_party/protobuf/<version>/src/google in the root of the Bazel tree.
4. cp -R <root of protobuf tree>/src/google/protobuf third_party/protobuf/src/google
5. Update the rules in third_party/protobuf/BUILD with the rules in the protobuf repository.

Finally, update the rules:

1. Add a BUILD file to third_party/protobuf/<version>/. Use the BUILD file for the previous version as a template. Update the cc_library rules to match the rules in the BUILD file in the protobuf repository. Also copy protobuf.bzl from the protobuf repository into third_party/protobuf/<version>/.
2. Modify third_party/protobuf/BUILD to point to the new rules.
3. Delete the old version of protobuf.

Updating anything else in the directory

Follow usual procedure as described on https://www.bazel.build/contributing.html