Use package:sky imports consistently

sky/sdk/lib/widgets/snack_bar.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 '../painting/text_style.dart';
-import '../theme/typography.dart' as typography;
-import 'basic.dart';
-import 'default_text_style.dart';
-import 'material.dart';
-import 'theme.dart';
+import 'package:sky/painting/text_style.dart';
+import 'package:sky/theme/typography.dart' as typography;
+import 'package:sky/widgets/basic.dart';
+import 'package:sky/widgets/default_text_style.dart';
+import 'package:sky/widgets/material.dart';
+import 'package:sky/widgets/theme.dart';
 
 class SnackBarAction extends Component {
   SnackBarAction({String key, this.label, this.onPressed }) : super(key: key) {
     assert(label != null);
   }
 
   final String label;
   final Function onPressed;
 
   Widget build() {
@@ skipping 40 matching lines @@
       child: new Container(
         margin: const EdgeDims.symmetric(horizontal: 24.0),
         child: new DefaultTextStyle(
           style: new TextStyle(color: Theme.of(this).accentColor),
           child: new Flex(children)
         )
       )
     );
   }
 }