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: /// Main entry point for commands.
  ///
  /// This function is intended to be used from the [flutter] command line tool.
  void main(List<String> args) {
    Logger.root.level = Level.WARNING;
    Logger.root.onRecord.listen((LogRecord record) {
      print('${record.level.name}: ${record.message}');
  
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';
  