Use an enum for Dart bindings for Skia Paint style

sky/sdk/lib/framework/components2/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 'package:sky/framework/theme2/colors.dart' as colors;
 
 import 'dart:sky' as sky;
 import '../fn2.dart';
 import '../rendering/box.dart';
 import '../rendering/object.dart';
@@ skipping 23 matching lines @@
     return new EventListenerNode(
       new Container(
         margin: const EdgeDims.symmetric(horizontal: 5.0),
         desiredSize: new sky.Size(diameter, diameter),
         child: new CustomPaint(
           callback: (RenderObjectDisplayList canvas) {
 
             sky.Paint paint = new sky.Paint()..color = color;
 
             // Draw the outer circle
-            paint.style = 1; // SkPaint::STROKE_STYLE;
+            paint.setStyle(sky.PaintingStyle.stroke);
             paint.strokeWidth = 2.0;
             canvas.drawCircle(outerRadius, outerRadius, outerRadius, paint);
 
             // Draw the inner circle
             if (value == groupValue) {
-              paint.style = 0; // SkPaint::FILL_STYLE;
+              paint.setStyle(sky.PaintingStyle.fill);
               canvas.drawCircle(outerRadius, outerRadius, innerRadius, paint);
             }
           }
         )
       ),
       onGestureTap: _handleClick
     );
   }
 
   void _handleClick(_) {
     onChanged(value);
   }
 }