Move animationgenerator.dart to sky/framework/animation/generator.dart

That's where it belongs.

R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/979283002

examples/fn/widgets/widgets.dart

@@ -2,6 +2,7 @@ library widgets;
 
 import '../../../framework/animation/curves.dart';
 import '../../../framework/animation/fling-curve.dart';
+import '../../../framework/animation/generator.dart';
 import '../../../framework/fn.dart';
 import '../../../framework/theme/colors.dart';
 import '../../../framework/theme/shadows.dart';
@@ -10,7 +11,6 @@ import 'dart:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
-part 'animationgenerator.dart';
 part 'box.dart';
 part 'button.dart';
 part 'buttonbase.dart';

examples/fn/widgets/animationgenerator.dart → framework/animation/generator.dart

-part of widgets;
+// 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.
 
-class FrameGenerator {
+import 'curves.dart';
+import 'dart:async';
+import 'dart:math' as math;
+import 'dart:sky' as sky;
 
+class FrameGenerator {
   Function onDone;
   StreamController _controller;
 
@@ -46,7 +52,6 @@ class FrameGenerator {
 }
 
 class AnimationGenerator extends FrameGenerator {
-
   Stream<double> get onTick => _stream;
   final double duration;
   final double begin;
@@ -62,12 +67,9 @@ class AnimationGenerator extends FrameGenerator {
     Function onDone
   }):super(onDone: onDone) {
     double startTime = 0.0;
-    double targetTime = 0.0;
     _stream = super.onTick.map((timeStamp) {
-      if (startTime == 0.0) {
+      if (startTime == 0.0)
         startTime = timeStamp;
-        targetTime = startTime + duration;
-      }
       return math.min((timeStamp - startTime) / duration, 1.0);
     })
     .takeWhile(_checkForCompletion)