Remove the pointless second argument to animate() in AnimatedValue.

sky/sdk/lib/widgets/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 'dart:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import '../animation/animated_value.dart';
@@ skipping 96 matching lines @@
 }
 
 class Drawer extends AnimatedComponent {
 
   Drawer({
     String key,
     this.controller,
     this.children,
     this.level: 0
   }) : super(key: key) {
-    animate(controller.position, (double value) {
-      _position = value;
-    });
+    watch(controller.position);
   }
 
   List<Widget> children;
   int level;
   DrawerController controller;
 
   void syncFields(Drawer source) {
     children = source.children;
     level = source.level;
     controller = source.controller;
     super.syncFields(source);
   }
 
-  double _position;
-
   Widget build() {
     Matrix4 transform = new Matrix4.identity();
-    transform.translate(_position);
+    transform.translate(controller.position.value);
 
-    double scaler = _position / _kWidth + 1;
+    double scaler = controller.position.value / _kWidth + 1;
     Color maskColor = new Color.fromARGB((0x7F * scaler).floor(), 0, 0, 0);
 
     var mask = new Listener(
       child: new Container(decoration: new BoxDecoration(backgroundColor: maskColor)),
       onGestureTap: controller.handleMaskTap,
       onGestureFlingStart: controller.handleFlingStart
     );
 
     Container content = new Container(
       decoration: new BoxDecoration(
         backgroundColor: Grey[50],
         boxShadow: shadows[level]),
       width: _kWidth,
       transform: transform,
       child: new Block(children)
     );
 
     return new Listener(
       child: new Stack([ mask, content ]),
       onPointerDown: controller.handlePointerDown,
       onPointerMove: controller.handlePointerMove,
       onPointerUp: controller.handlePointerUp,
       onPointerCancel: controller.handlePointerCancel
     );
   }
 
 }