Break dependency of AnimationPerformance on AnimatedValue

sky/sdk/example/widgets/card_collection.dart

Index: sky/sdk/example/widgets/card_collection.dart
diff --git a/sky/sdk/example/widgets/card_collection.dart b/sky/sdk/example/widgets/card_collection.dart
index 13330e022f93f199cd5c37290893e795af9ac246..9d0971590c0e804d6e23937c2b549eb753c26e62 100644
--- a/sky/sdk/example/widgets/card_collection.dart
+++ b/sky/sdk/example/widgets/card_collection.dart
@@ -29,8 +29,8 @@ class CardCollectionApp extends App {
   CardCollectionApp() {
     _activeCardAnimation = new AnimationPerformance()
       ..variable = new AnimatedType(0.0, 1.0)
-      ..duration = new Duration(milliseconds: _kCardDismissFadeoutMS);
-    _activeCardAnimation.timeline.onValueChanged.listen(_handleAnimationProgressChanged);
+      ..duration = new Duration(milliseconds: _kCardDismissFadeoutMS)
+      ..addListener(_handleAnimationProgressChanged);
   }
 
   int _activeCardIndex = -1;
@@ -46,7 +46,7 @@ class CardCollectionApp extends App {
     return _activeCardAnimation.progress * _activeCardDragX.sign * _activeCardWidth * _kDismissCardThreshold;
   }
 
-  void _handleAnimationProgressChanged(_) {
+  void _handleAnimationProgressChanged() {
     setState(() {
       if (_activeCardAnimation.isCompleted && !_activeCardDragUnderway)
         _dismissedCardIndices.add(_activeCardIndex);