Make isEmpty a getter.

tests/html/element_classes_test.dart

 // Copyright (c) 2011, 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('ElementTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
@@ skipping 71 matching lines @@
         makeClassSet().every((c) => c.contains('a')));
   });
 
   test('some', () {
     Expect.isTrue(
         makeClassSet().some((c) => c.contains('a')));
     Expect.isFalse(makeClassSet().some((c) => c is num));
   });
 
   test('isEmpty', () {
-    Expect.isFalse(makeClassSet().isEmpty());
-    Expect.isTrue(makeElement().classes.isEmpty());
+    Expect.isFalse(makeClassSet().isEmpty);
+    Expect.isTrue(makeElement().classes.isEmpty);
   });
 
   test('length', () {
     Expect.equals(3, makeClassSet().length);
     Expect.equals(0, makeElement().classes.length);
   });
 
   test('contains', () {
     Expect.isTrue(makeClassSet().contains('foo'));
     Expect.isFalse(makeClassSet().contains('qux'));
@@ skipping 57 matching lines @@
     Expect.setEquals(['foo', 'baz'],
         classes.intersection(['foo', 'qux', 'baz']));
   });
 
   test('clear', () {
     final classes = makeClassSet();
     classes.clear();
     Expect.setEquals([], classes);
   });
 }