Make arg parser return growable list of rest arguments.

pkg/args/lib/src/parser.dart

 // Copyright (c) 2013, 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 args.src.parser;
 
 import '../args.dart';
 
 final _SOLO_OPT = new RegExp(r'^-([a-zA-Z0-9])$');
 final _ABBR_OPT = new RegExp(r'^-([a-zA-Z0-9]+)(.*)$');
@@ skipping 77 matching lines @@
     grammar.options.forEach((name, option) {
       if (option.allowMultiple &&
           results[name].length == 0 &&
           option.defaultValue != null) {
         results[name].add(option.defaultValue);
       }
       if (option.callback != null) option.callback(results[name]);
     });
 
     // Add in the leftover arguments we didn't parse to the innermost command.
-    var rest = args.toList();
+    var rest = args.toList(growable: true);
     args.clear();
     return new ArgResults(results, commandName, commandResults, rest);
   }
 
   /**
    * Pulls the value for [option] from the second argument in [args]. Validates
    * that there is a valid value there.
    */
   void readNextArgAsValue(Option option) {
     // Take the option argument from the next command line arg.
@@ skipping 163 matching lines @@
           '"$value" is not an allowed value for option "${option.name}".');
     }
 
     if (option.allowMultiple) {
       results[option.name].add(value);
     } else {
       results[option.name] = value;
     }
   }
 }