Make isEmpty a getter.

utils/archive/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('options');
 
 /**
  * An individual option.
  */
 class ArchiveOption {
@@ skipping 12 matching lines @@
 /**
  * A collection of options.
  */
 class ArchiveOptions {
   /** The internal options map. */
   final Map<String, ArchiveOption> _options;
 
   ArchiveOptions() : _options = <String, ArchiveOption>{};
 
   /** Returns whether any options have been set. */
-  bool get isEmpty => _options.isEmpty();
+  bool get isEmpty => _options.isEmpty;
 
   /**
    * Sets an option. [value] should either be a bool or something with a
    * reasonable `toString` method.
    *
    * To set the module for an option, use [operator[]].
    */
   void operator[]=(String name, value) {
     _options[name] = new ArchiveOption(name, value);
   }
 
   /** Gets the option with the given name. */
   ArchiveOption operator[](String name) {
     return _options[name];
   }
 
   /** Gets all options. */
   List<ArchiveOption> get all => _options.getValues();
 }