Use package:sky imports consistently

sky/sdk/lib/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 '../animation/animation_performance.dart';
-import 'basic.dart';
+import 'package:sky/animation/animation_performance.dart';
+import 'package:sky/widgets/basic.dart';
 
 abstract class AnimatedComponent extends StatefulComponent {
 
   AnimatedComponent({ String key }) : super(key: key);
 
   void syncFields(AnimatedComponent source) { }
 
   final List<AnimationPerformance> _watchedPerformances = new List<AnimationPerformance>();
 
   void watchPerformance(AnimationPerformance performance) {
     assert(!_watchedPerformances.contains(performance));
     _watchedPerformances.add(performance);
     if (mounted)
       performance.addListener(scheduleBuild);
   }
 
   void didMount() {
     for (AnimationPerformance performance in _watchedPerformances)
       performance.addListener(scheduleBuild);
     super.didMount();
   }
 
   void didUnmount() {
     for (AnimationPerformance performance in _watchedPerformances)
       performance.removeListener(scheduleBuild);
     super.didUnmount();
   }
 
 }