anchor.diff:  
     @override
     Future<int> run() async {
  -    if (argResults['mojo-path'] == null && !argResults['android']) {
  -      _logging.severe('Must specify --mojo-path for Linux.');
  +    if (argResults['mojo-path'] == null) {
  +      _logging.severe('Must specify --mojo-path.');
         return 1;
       }
   
  -    if (argResults['devtools-path'] == null && argResults['android']) {
  -      _logging.severe('Must specify --devtools-path for Android.');
  -      return 1;
  -    }
       if (argResults['mojo-debug'] && argResults['mojo-release']) {
         _logging.severe('Cannot specify both --mojo-debug and --mojo-release');
         return 1;
  
positive.code: 
      args.addAll(argResults.rest);
      if (argResults['android']) {
        return _runAndroid(argResults['devtools-path'], mojoConfig, appPath, args);
      } else {
        return _runLinux(mojoPath, mojoConfig, appPath, args);
      }
  
negative.code:     argParser.addFlag('mojo-release', negatable: false, help: 'Use Release build of mojo (default)');
  
      argParser.addOption('app', defaultsTo: 'app.flx');
      argParser.addOption('mojo-path', help: 'Path to directory containing mojo_shell and services for Linux and to mojo devtools from Android.');
    }
  
    // TODO(abarth): Why not use path.absolute?
  