[Effen] Reduce splashes when scrolling.

sky/framework/animation/generators.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 'dart:math' as math;
 import 'dart:sky' as sky;
 import 'mechanics.dart';
 
@@ skipping 50 matching lines @@
   Stream<double> get onTick => _stream;
   final double initialDelay;
   final double duration;
   final double begin;
   final double end;
   final Curve curve;
 
   FrameGenerator _generator;
   Stream<double> _stream;
   bool _done = false;
+  double _lastTime;
 
   AnimationGenerator({
     this.initialDelay: 0.0,
     this.duration,
     this.begin: 0.0,
     this.end: 1.0,
     this.curve: linear,
     Function onDone
   }) {
     assert(curve != null);
     assert(duration != null && duration > 0.0);
     _generator = new FrameGenerator(onDone: onDone);
 
     double startTime = 0.0;
     _stream = _generator.onTick.map((timeStamp) {
       if (startTime == 0.0)
         startTime = timeStamp;
 
       double t = (timeStamp - (startTime + initialDelay)) / duration;
-      return math.max(0.0, math.min(t, 1.0));
+      _lastTime = math.max(0.0, math.min(t, 1.0));
+      return _lastTime;
     })
     .takeWhile(_checkForCompletion)
     .where((t) => t >= 0.0)
     .map(_transform);
   }
 
+  double get remainingTime {
+    if (_lastTime == null)
+      return duration;
+    return duration - _lastTime;
+  }
+
   void cancel() {
     _generator.cancel();
   }
 
   double _transform(double t) {
     if (_done)
       return end;
     return begin + (end - begin) * curve.transform(t);
   }
 
@@ skipping 37 matching lines @@
   double _update(double timeStamp) {
     double previousTime = _previousTime;
     _previousTime = timeStamp;
     if (previousTime == 0.0)
       return timeStamp;
     double deltaT = timeStamp - previousTime;
     system.update(deltaT);
     return timeStamp;
   }
 }