Make isEmpty a getter.

tests/compiler/dart2js/link_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.
 
 import '../../../lib/compiler/implementation/util/util.dart';
 import '../../../lib/compiler/implementation/util/util_implementation.dart';
 
 main() {
   test(const Link<Comparable>().prepend('three').prepend(2).prepend('one'),
        ['one', 2, 'three']);
   test(const Link<Comparable>().prepend(3).prepend('two').prepend(1),
        [1, 'two', 3]);
   test(const Link<String>().prepend('single'), ['single']);
   test(const Link(), []);
   testFromList([]);
   testFromList([0]);
   testFromList([0, 1]);
   testFromList([0, 1, 2]);
   testFromList([0, 1, 2, 3]);
   testFromList([0, 1, 2, 3, 4]);
   testFromList([0, 1, 2, 3, 4, 5]);
 }
 
 testFromList(List list) {
   test(new Link.fromList(list), list);
 }
 
 test(Link link, List list) {
-  Expect.equals(list.isEmpty(), link.isEmpty());
+  Expect.equals(list.isEmpty, link.isEmpty);
   int i = 0;
   for (var element in link.toList()) {
     Expect.equals(list[i++], element);
   }
   Expect.equals(list.length, i);
   i = 0;
   for (var element in link) {
     Expect.equals(list[i++], element);
   }
   Expect.equals(list.length, i);
   i = 0;
-  for (; !link.isEmpty(); link = link.tail) {
+  for (; !link.isEmpty; link = link.tail) {
     Expect.equals(list[i++], link.head);
   }
   Expect.equals(list.length, i);
-  Expect.isTrue(link.isEmpty());
+  Expect.isTrue(link.isEmpty);
 }