Move AnimatedComponent away from mirrors and towards a callback-based setter.

sky/sdk/lib/framework/components2/drawer.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 '../animation/animated_value.dart';
 import '../animation/curves.dart';
 import '../fn2.dart';
 import '../theme2/colors.dart';
 import '../theme2/shadows.dart';
 import 'animated_component.dart';
@@ skipping 86 matching lines @@
   DrawerController controller;
 
   double _position;
 
   Drawer({
     Object key,
     this.controller,
     this.children,
     this.level: 0
   }) : super(key: key) {
-    animateField(controller.position, #_position);
+    animate(controller.position, (double value) {
+      _position = value;
+    });
   }
 
   UINode build() {
     Matrix4 transform = new Matrix4.identity();
     transform.translate(_position);
 
     double scaler = _position / _kWidth + 1;
     Color maskColor = new Color.fromARGB((0x7F * scaler).floor(), 0, 0, 0);
 
     var mask = new EventListenerNode(
@@ skipping 15 matching lines @@
       new StackContainer(
         children: [ mask, content ]
       ),
       onPointerDown: controller.handlePointerDown,
       onPointerMove: controller.handlePointerMove,
       onPointerUp: controller.handlePointerUp,
       onPointerCancel: controller.handlePointerCancel
     );
   }
 }