Switch scroll physics over to using newton

sky/sdk/lib/animation/animated_simulation.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:async';
+
+import 'package:newton/newton.dart';
+
+import 'timeline.dart';
+
+const double _kSecondsPerMillisecond = 1000.0;
+
+class AnimatedSimulation {
+
+  AnimatedSimulation(Function onTick) : _onTick = onTick {
+    _ticker = new Ticker(_tick);
+  }
+
+  final Function _onTick;
+  Ticker _ticker;
+
+  Simulation _simulation;
+  double _startTime;
+
+  double _value = 0.0;
+  double get value => _value;
+
+  Future start(Simulation simulation) {
+    assert(simulation != null);
+    assert(!_ticker.isTicking);
+    _simulation = simulation;
+    _startTime = null;
+    _value = simulation.x(0.0);
+    return _ticker.start();
+  }
+
+  void stop() {
+    _simulation = null;
+    _startTime = null;
+    _value = 0.0;
+    _ticker.stop();
+  }
+
+  bool get isAnimating => _ticker.isTicking;
+
+  void _tick(double timeStamp) {
+    if (_startTime == null)
+      _startTime = timeStamp;
+
+    double timeInSeconds = (timeStamp - _startTime) / _kSecondsPerMillisecond;
+    _value = _simulation.x(timeInSeconds);
+    final bool isLastTick = _simulation.isDone(timeInSeconds);
+
+    _onTick(_value);
+
+    if (isLastTick)
+      stop();
+  }
+
+}