clean up API for file_generator.dart

lib/code_generator.dart

Index: lib/code_generator.dart
diff --git a/lib/code_generator.dart b/lib/code_generator.dart
index 92561a43d97385b7efe5df6605e33c2d00f865e8..2f3f92cc664804641c815f533e1c35013cfbf53a 100644
--- a/lib/code_generator.dart
+++ b/lib/code_generator.dart
@@ -65,9 +65,7 @@ class CodeGenerator extends ProtobufContainer {
       for (var gen in generators) {
         var name = gen._fileDescriptor.name;
         if (request.fileToGenerate.contains(name)) {
-          response.file.add(gen.generateResponse(config));
-          response.file.add(gen.generateEnumResponse(config));
-          response.file.add(gen.generateJsonDartResponse(config));
+          response.file.addAll(gen.generateFiles(config));
         }
       }
       _streamOut.add(response.writeToBuffer());