Use package:sky imports consistently

sky/sdk/lib/widgets/switch.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:sky' as sky;
 
+import 'package:sky/painting/shadows.dart';
+import 'package:sky/rendering/box.dart';
 import 'package:sky/theme/shadows.dart';
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/theme.dart';
+import 'package:sky/widgets/toggleable.dart';
 
-import '../painting/shadows.dart';
-import '../rendering/box.dart';
-import 'basic.dart';
-import 'theme.dart';
-import 'toggleable.dart';
-export 'toggleable.dart' show ValueChanged;
+export 'package:sky/widgets/toggleable.dart' show ValueChanged;
 
 const sky.Color _kThumbOffColor = const sky.Color(0xFFFAFAFA);
 const sky.Color _kTrackOffColor = const sky.Color(0x42000000);
 const double _kSwitchWidth = 35.0;
 const double _kThumbRadius = 10.0;
 const double _kSwitchHeight = _kThumbRadius * 2.0;
 const double _kTrackHeight = 14.0;
 const double _kTrackRadius = _kTrackHeight / 2.0;
 const double _kTrackWidth = _kSwitchWidth - (_kThumbRadius - _kTrackRadius) * 2.0;
 
@@ skipping 37 matching lines @@
 
     // The thumb contracts slightly during the animation
     double inset = 2.0 - (position.value - 0.5).abs() * 2.0;
     Point thumbPos = new Point(
       _kTrackRadius + position.value * (_kTrackWidth - _kTrackRadius * 2),
       _kSwitchHeight / 2.0
     );
     canvas.drawCircle(thumbPos, _kThumbRadius - inset, paint);
   }
 }