Refactor stateful parts of Component into StatefulComponent

sky/sdk/lib/widgets/animated_component.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:async';
 
 import 'package:vector_math/vector_math.dart';
 
 import '../animation/animated_value.dart';
 import '../animation/animation_performance.dart';
 import '../animation/curves.dart';
 import 'basic.dart';
 
 class _AnimationEntry {
   _AnimationEntry(this.value);
   final AnimatedValue value;
   StreamSubscription<double> subscription;
 }
 
-abstract class AnimatedComponent extends Component {
+abstract class AnimatedComponent extends StatefulComponent {
 
-  AnimatedComponent({ String key }) : super(key: key, stateful: true);
+  AnimatedComponent({ String key }) : super(key: key);
 
   void syncFields(AnimatedComponent source) { }
 
   List<_AnimationEntry> _animatedFields = new List<_AnimationEntry>();
 
   watch(AnimatedValue value) {
     assert(!mounted);
     // TODO(ianh): we really should assert that we're not doing this
     // in the constructor since doing it there is pointless and
     // expensive, since we'll be doing it for every copy of the object
@@ skipping 33 matching lines @@
 class AnimatedPosition extends AnimatedType<Point> {
   AnimatedPosition(Point begin, Point end, {Curve curve: linear})
       : super(begin, end, curve: curve);
 
   Widget build(Widget child) {
     Matrix4 transform = new Matrix4.identity();
     transform.translate(value.x, value.y);
     return new Transform(transform: transform, child: child);
   }
 }