Rationalize Dart mojo and sky package structure

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 'curves.dart';
-import 'dart:async';
-import 'generators.dart';
-
-typedef void Callback ();
-
-class AnimatedValue {
-  StreamController _controller = new StreamController.broadcast(sync: true);
-  AnimationGenerator _animation;
-  Completer _completer;
-  double _value;
-
-  AnimatedValue(double initial, { Callback onChange }) {
-    _value = initial;
-    _onChange = onChange;
-  }
-  Callback _onChange;
-
-  // 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);
-    if (_onChange != null)
-      _onChange();
-  }
-
-  void _done() {
-    _animation = null;
-    if (_completer == null)
-      return;
-    Completer completer = _completer;
-    _completer = null;
-    completer.complete(_value);
-  }
-
-  void stop() {
-    if (_animation != null) {
-      _animation.cancel(); // will call _done() if it isn't already finished
-      _done();
-    }
-  }
-
-  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)
-      ..onTick.listen(_setValue, onDone: _done);
-
-    _completer = new Completer();
-    return _completer.future;
-  }
-
-  double get remainingTime {
-    if (_animation == null)
-      return 0.0;
-    return _animation.remainingTime;
-  }
-
-}