Rationalize Dart mojo and sky package structure

sky/sdk/lib/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 'ink_well.dart';
 
 typedef void ValueChanged(value);
 
@@ skipping 43 matching lines @@
         highlight ? _highlightStyle : _style
       ),
       onGestureTap: _handleClick
     );
   }
 
   void _handleClick(_) {
     onChanged(value);
   }
 }