anchor.diff:        skiaserveUri = Uri.parse(argResults['skiaserve']);
       } else {
         printError('Must provide --output-file or --skiaserve');
  +      return 1;
  +    }
  +    if (argResults['diagnostic-port'] == null) {
  +      printError('Must provide --diagnostic-port');
         return 1;
       }
   
  
positive.code: 
  import 'package:http/http.dart' as http;
  
  import '../base/common.dart';
  import '../globals.dart';
  import '../runner/flutter_command.dart';
  
  
negative.code:     argParser.addOption('output-file', help: 'Write the Skia picture file to this path.');
      argParser.addOption('skiaserve', help: 'Post the picture to a skiaserve debugger at this URL.');
      argParser.addOption('diagnostic-port',
          help: 'Local port where the diagnostic server is listening.');
    }
  
  