Make Map.keys/values Iterables.

pkg/args/lib/args.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.
 
 /**
  * This library lets you define parsers for parsing raw command-line arguments
  * into a set of options and values using [GNU][] and [POSIX][] style options.
  *
  * ## Defining options ##
  *
@@ skipping 526 matching lines @@
   operator [](String name) {
     if (!_options.containsKey(name)) {
       throw new ArgumentError(
           'Could not find an option named "$name".');
     }
 
     return _options[name];
   }
 
   /** Get the names of the options as a [Collection]. */
-  Collection<String> get options => _options.keys;
+  Collection<String> get options => _options.keys.toList();
 }
 
 class _Option {
   final String name;
   final String abbreviation;
   final List allowed;
   final defaultValue;
   final Function callback;
   final String help;
   final Map<String, String> allowedHelp;
@@ skipping 218 matching lines @@
       allowedBuffer.add(allowed);
       if (allowed == option.defaultValue) {
         allowedBuffer.add(' (default)');
       }
       first = false;
     }
     allowedBuffer.add(']');
     return allowedBuffer.toString();
   }
 }