Rationalize Dart mojo and sky package structure

sky/framework/elements/animation/controller.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/curves.dart";
-import "timer.dart";
-
-class AnimationController extends AnimationDelegate {
-  final AnimationDelegate _delegate;
-  AnimationTimer _timer;
-  double _begin = 0.0;
-  double _end = 0.0;
-  Curve _curve;
-  bool _isAnimating = false;
-
-  AnimationController(this._delegate) {
-    _timer = new AnimationTimer(this);
-  }
-
-  bool get isAnimating => _isAnimating;
-
-  void start({double begin: 0.0, double end: 0.0, Curve curve: linear,
-              double duration: 0.0}) {
-    _begin = begin;
-    _end = end;
-    _curve = curve;
-    _isAnimating = true;
-    _timer.start(duration);
-  }
-
-  void stop() {
-    _isAnimating = false;
-    _timer.stop();
-  }
-
-  double _positionForTime(double t) {
-    // Explicitly finish animations at |_end| in case the curve isn't an
-    // exact numerical transform.
-    if (t == 1)
-      return _end;
-    double curvedTime = _curve.transform(t);
-    return _begin + (_end - _begin) * curvedTime;
-  }
-
-  void updateAnimation(double t) {
-    _delegate.updateAnimation(_positionForTime(t));
-  }
-}