Make isEmpty a getter.

samples/ui_lib/base/AnimationScheduler.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.
 
 typedef void AnimationCallback(num currentTime);
 
 class CallbackData {
   final AnimationCallback callback;
   final num minTime;
   int id;
@@ skipping 92 matching lines @@
           _webkitAnimationFrameMaybeAvailable = false;
         }
       }
       if (!_webkitAnimationFrameMaybeAvailable) {
         _intervalId = window.setTimeout(() { _step(); }, MS_PER_FRAME);
       }
     }
   }
 
   void _step() {
-    if (_callbacks.isEmpty()) {
+    if (_callbacks.isEmpty) {
       // Cancel the interval on the first frame where there aren't actually
       // any available callbacks.
       assert(_intervalId != null);
       if (USE_INTERVALS) {
         window.clearInterval(_intervalId);
       }
       _intervalId = null;
     } else if (USE_INTERVALS == false) {
       _intervalId = null;
       _setupInterval();
@@ skipping 33 matching lines @@
     _frameCount++;
     if (_isMobileSafari) {
       // Hack to work around an iOS bug where sometimes animations do not
       // render if only webkit transforms were modified.
       // TODO(jacobr): find a cleaner workaround.
       int offset = _frameCount % 2;
       _safariHackStyle.left = '${offset}px';
     }
   }
 }