Make isEmpty a getter.

tests/html/query_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('QueryTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
@@ skipping 30 matching lines @@
   test('queryAll (Multiple)', () {
       List l = queryAll('img');
       Expect.equals(2, l.length);
       Expect.isTrue(l[0] is ImageElement);
       Expect.isTrue(l[1] is ImageElement);
       Expect.notEquals(l[0], l[1]);
     });
 
   test('queryAll (None)', () {
       List l = queryAll('video');
-      Expect.isTrue(l.isEmpty());
+      Expect.isTrue(l.isEmpty);
     });
 }