Refactor fn2.dart, since it breached our 1000-line threshold.

sky/sdk/lib/framework/widgets/scrollable.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:math' as math;
+import 'dart:sky' as sky;
+
 import '../animation/generators.dart';
 import '../animation/mechanics.dart';
 import '../animation/scroll_behavior.dart';
-import '../fn2.dart';
 import '../theme/view_configuration.dart' as config;
-import 'dart:math' as math;
-import 'dart:sky' as sky;
+import 'wrappers.dart';
 
 const double _kMillisecondsPerSecond = 1000.0;
 
 double _velocityForFlingGesture(sky.GestureEvent event) {
   return math.max(-config.kMaxFlingVelocity, math.min(config.kMaxFlingVelocity,
       -event.velocityY)) / _kMillisecondsPerSecond;
 }
 
 abstract class ScrollClient {
   bool ancestorScrolled(Scrollable ancestor);
@@ skipping 121 matching lines @@
 
   void _handleFlingCancel(sky.GestureEvent event) {
     _startSimulation(_createParticle());
   }
 
   void _handleWheel(sky.WheelEvent event) {
     scrollBy(-event.offsetY);
   }
 
 }