Added a header only cc_library target for the protobuf library.
Added a header only cc_library target for the protobuf library.

google/protobuf,google/protobuf,google/protobuf,Livefyre/protobuf,Livefyre/protobuf,Livefyre/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,Livefyre/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,Livefyre/protobuf