Animate checkboxes

sky/sdk/lib/framework/widgets/wrappers.dart

Index: sky/sdk/lib/framework/widgets/wrappers.dart
diff --git a/sky/sdk/lib/framework/widgets/wrappers.dart b/sky/sdk/lib/framework/widgets/wrappers.dart
index 75eeb03fe06d4be7632f2292bc622bd718ea7c72..1d51903f6d504dd57d3e673887fd5cb63c449e5a 100644
--- a/sky/sdk/lib/framework/widgets/wrappers.dart
+++ b/sky/sdk/lib/framework/widgets/wrappers.dart
@@ -49,19 +49,21 @@ class DecoratedBox extends OneChildRenderObjectWrapper {
 
 }
 
-// TODO(jackson) need a mechanism for marking the RenderCustomPaint as needing paint
 class CustomPaint extends OneChildRenderObjectWrapper {
 
-  CustomPaint({ this.callback, UINode child, Object key })
+  CustomPaint({ this.callback, this.token, UINode child, Object key })
     : super(child: child, key: key);
 
   RenderCustomPaint get root { RenderCustomPaint result = super.root; return result; }
   final CustomPaintCallback callback;
+  final dynamic token;  // set this to be repainted automatically when the token changes
 
   RenderCustomPaint createNode() => new RenderCustomPaint(callback: callback);
 
   void syncRenderObject(CustomPaint old) {
     super.syncRenderObject(old);
+    if (old != null && old.token != token)
+      root.markNeedsPaint();
     root.callback = callback;
   }