Make isEmpty a getter.

tests/html/xmlelement_test.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('XMLElementTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 main() {
@@ skipping 118 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 412 matching lines @@
     });
   });
 
   test('default rect values', () {
     makeElement().rect.then(
       expectAsync1(ElementRect rect) {
         expectEmptyRect(rect.client);
         expectEmptyRect(rect.offset);
         expectEmptyRect(rect.scroll);
         expectEmptyRect(rect.bounding);
-        Expect.isTrue(rect.clientRects.isEmpty());
+        Expect.isTrue(rect.clientRects.isEmpty);
       }));
   });
 }