Menu in StocksApp should animate out

sky/framework/animation/animated_value.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 '../fn.dart';
 import 'curves.dart';
 import 'dart:async';
 import 'generators.dart';
 
 class AnimatedValue {
   StreamController _controller = new StreamController(sync: true);
   AnimationGenerator _animation;
+  Completer _completer;
   double _value;
 
   AnimatedValue(double initial) {
     _value = initial;
   }
 
   // A stream of change in value from |initial|. The stream does not
   // contain the initial value. Consumers should check the initial value via
   // the |value| accessor.
   Stream<double> get onValueChanged => _controller.stream;
 
   double get value => _value;
 
   void set value(double value) {
     stop();
    _setValue(value);
   }
 
   bool get isAnimating => _animation != null;
 
   void _setValue(double value) {
     _value = value;
     _controller.add(_value);
   }
 
+  void _done() {
+    _animation = null;
+    if (_completer == null)
+      return;
+    Completer completer = _completer;
+    _completer = null;
+    completer.complete(_value);
+  }
+
   void stop() {
     if (_animation != null) {
       _animation.cancel();
-      _animation = null;
+      _done();
     }
   }
 
-  void animateTo(double newValue, double duration,
+  Future<double> animateTo(double newValue, double duration,
       { Curve curve: linear, double initialDelay: 0.0 }) {
     stop();
 
     _animation = new AnimationGenerator(
         duration: duration,
         begin: _value,
         end: newValue,
         curve: curve,
-        initialDelay: initialDelay);
+        initialDelay: initialDelay)
+      ..onTick.listen(_setValue, onDone: _done);
 
-    _animation.onTick.listen(_setValue, onDone: () {
-      _animation = null;
-    });
+    _completer = new Completer();
+    return _completer.future;
   }
 }