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

sky/sdk/lib/framework/widgets/animated_component.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 '../animation/animated_value.dart';
-import '../fn2.dart';
-import 'dart:async';
+import 'wrappers.dart';
 
 typedef void SetterFunction(double value);
 
 class _AnimationEntry {
   _AnimationEntry(this.value, this.setter);
   final AnimatedValue value;
   final SetterFunction setter;
   StreamSubscription<double> subscription;
 }
 
@@ skipping 24 matching lines @@
   void didUnmount() {
     for (_AnimationEntry entry in _animatedFields) {
       assert(entry.subscription != null);
       entry.subscription.cancel();
       entry.subscription = null;
     }
     super.didUnmount();
   }
 
 }