These are the protobuf definition files used by the region grouping feature.
The protos here are used by the region grouping coprocessor endpoints.

The produced java classes are generated and then checked in. The reasoning
is that they change infrequently and it saves generating anew on each build.

To regenerate the classes after making definition file changes, ensure first that
the protobuf protoc tool is in your $PATH. You may need to download it and build
it first; its part of the protobuf package. For example, if using v2.5.0 of
protobuf, it is obtainable from here:

 https://github.com/google/protobuf/releases/tag/v2.5.0

HBase uses hadoop-maven-plugins:protoc goal to invoke the protoc command. You can
compile the protoc definitions by invoking maven with profile compile-protobuf or
passing in compile-protobuf property.

mvn compile -Dcompile-protobuf
or
mvn compile -Pcompile-protobuf

You may also want to define protoc.path for the protoc binary

mvn compile -Dcompile-protobuf -Dprotoc.path=/opt/local/bin/protoc

If you have added a new proto file, you should add it to the pom.xml file first.
Other modules also support the maven profile.

After you've done the above, check it in and then check it in (or post a patch
on a JIRA with your definition file changes and the generated files).