Fix errors in Sky detected by Dart analyzer

sky/framework/components/radio.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 '../fn.dart';
 import 'button_base.dart';
 import 'material.dart';
 
 typedef void ValueChanged(value);
 
@@ skipping 39 matching lines @@
     this.onChanged,
     this.value,
     this.groupValue
   }) : super(key: key) {
     events.listen('click', _handleClick);
   }
 
   Node build() {
     return new Material(
       styles: [highlight ? _highlightStyle : _style],
-      children: value == groupValue ? [new Container( style : _dotStyle )] : []
-    )
+      children: value == groupValue ? [new Container(styles: [_dotStyle] )] : []
+    );
   }
 
   void _handleClick(_) {
     onChanged(value);
   }
 }