Fix 'error: a class-key must be used when declaring a friend' compile error.
Fix 'error: a class-key must be used when declaring a friend' compile error.

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