Make GeneratedMessage abstract
Make GeneratedMessage abstract

google/protobuf.dart,dart-lang/dart-protobuf,google/protobuf.dart,dart-lang/protobuf,dart-lang/protobuf,dart-lang/protobuf,dart-lang/dart-protobuf,collinjackson/dart-protobuf,google/protobuf.dart,dart-lang/dart-protobuf