Make isEmpty a getter.

tests/standalone/io/directory_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.
 //
 // Directory listing test.
 
 #import("dart:io");
 #import("dart:isolate");
 
 class DirectoryTest {
@@ skipping 396 matching lines @@
     if (createdDirectories.length < nestingDepth) {
       temp = new Directory(
           '${temp.path}/nested_temp_dir_${createdDirectories.length}_');
       temp.createTemp().then(createPhaseCallback);
     } else {
       deletePhaseCallback();
     }
   }
 
   void deletePhaseCallback() {
-    if (!createdDirectories.isEmpty()) {
+    if (!createdDirectories.isEmpty) {
       current = createdDirectories.removeLast();
       current.deleteSync();
       deletePhaseCallback();
     }
   }
 
   static void testMain() {
     new NestedTempDirectoryTest.run();
     new NestedTempDirectoryTest.run();
   }
@@ skipping 132 matching lines @@
   DirectoryTest.testMain();
   NestedTempDirectoryTest.testMain();
   testCreateTempErrorSync();
   testCreateTempError();
   testCreateExistingSync();
   testCreateExisting();
   testCreateDirExistingFileSync();
   testCreateDirExistingFile();
   testRename();
 }