anchor.diff:      ..addCommand(new RunMojoCommand())
       ..addCommand(new StartCommand())
       ..addCommand(new StopCommand())
  -    ..addCommand(new TraceCommand())
  -    ..run(args);
  +    ..addCommand(new TraceCommand());
  +
  +  try {
  +    await runner.run(args);
  +  } on UsageException catch (e) {
  +    print(e);
  +    exit(1);
  +  }
   }
  
positive.code:       print(record.stackTrace);
    });
  
    new FlutterCommandRunner()
      ..addCommand(new BuildCommand())
      ..addCommand(new CacheCommand())
      ..addCommand(new InitCommand())
  
negative.code: // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  import 'dart:async';
  import 'dart:io';
  
  import 'package:args/command_runner.dart';
  import 'package:logging/logging.dart';
  
  import 'src/commands/flutter_command_runner.dart';
  