Make performance and position private since they don’t sync

sky/sdk/lib/widgets/toggleable.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:sky' as sky;
 
 import '../animation/animation_performance.dart';
 import '../animation/curves.dart';
 import 'animated_component.dart';
 import 'basic.dart';
 
 typedef void ValueChanged(value);
 
 const Duration _kCheckDuration = const Duration(milliseconds: 200);
 
 abstract class Toggleable extends AnimatedComponent {
 
   Toggleable({
     String key,
     this.value,
     this.onChanged
   }) : super(key: key) {
-    position = new AnimatedType<double>(0.0, end: 1.0);
-    performance = new AnimationPerformance()
+    _position = new AnimatedType<double>(0.0, end: 1.0);
+    _performance = new AnimationPerformance()
       ..variable = position
       ..duration = _kCheckDuration
       ..progress = value ? 1.0 : 0.0;
     watchPerformance(performance);
   }
 
   bool value;
   ValueChanged onChanged;
 
-  AnimatedType<double> position;
-  AnimationPerformance performance;
+  AnimatedType<double> _position;
+  AnimatedType<double> get position => _position;
+
+  AnimationPerformance _performance;
+  AnimationPerformance get performance => _performance;
 
   void syncFields(Toggleable source) {
     onChanged = source.onChanged;
     if (value != source.value) {
       value = source.value;
       // TODO(abarth): Setting the curve on the position means there's a
       // discontinuity when we reverse the timeline.
       if (value) {
         position.curve = curveUp;
         performance.play();
@@ skipping 27 matching lines @@
         height: size.height,
         child: new CustomPaint(
           token: position.value,
           callback: customPaintCallback
         )
       ),
       onGestureTap: _handleClick
     );
   }
 }