pkg/csslib: fixes for args

lib/src/options.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library csslib.src.options;
 
 import 'package:args/args.dart';
 
 class PreprocessorOptions {
   /** Generate polyfill code (e.g., var, etc.) */
@@ skipping 20 matching lines @@
    * Less syntax supported:
    * - @name at root level statically defines variables resolved at compilation
    * time.  Essentially a directive e.g., @var-name.
    */
   final bool lessSupport;
 
   /** Whether to use colors to print messages on the terminal. */
   final bool useColors;
 
   /** File to process by the compiler. */
-  String inputFile;
+  final String inputFile;
 
-  // We could make this faster, if it ever matters.
-  factory PreprocessorOptions() => parse(['']);
+  const PreprocessorOptions({this.verbose: false, this.checked: false,
+      this.lessSupport: true, this.warningsAsErrors: false,
+      this.throwOnErrors: false, this.throwOnWarnings: false,
+      this.useColors: true, this.polyfill: false, this.inputFile});
 
   PreprocessorOptions.fromArgs(ArgResults args)
       : warningsAsErrors = args['warnings_as_errors'],
         throwOnWarnings = args['throw_on_warnings'],
         throwOnErrors = args['throw_on_errors'],
         verbose = args['verbose'],
         checked = args['checked'],
         lessSupport = args['less'],
         useColors = args['colors'],
         polyfill = args['polyfill'],
@@ skipping 45 matching lines @@
       showUsage(parser);
       return null;
     }
   }
 
   static showUsage(parser) {
     print('Usage: css [options...] input.css');
     print(parser.getUsage());
   }
 }