Remove one more use of mirrors: Components now have to explicitly sync their fields.

sky/sdk/lib/framework/components2/material.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 '../fn2.dart';
 import '../theme/shadows.dart';
 
 class Material extends Component {
 
   Material({ Object key, this.content, this.level: 0 }) : super(key: key);
 
   // static final List<Style> _shadowStyle = [
   //   null,
   //   new Style('box-shadow: ${Shadow[1]}'),
   //   new Style('box-shadow: ${Shadow[2]}'),
   //   new Style('box-shadow: ${Shadow[3]}'),
   //   new Style('box-shadow: ${Shadow[4]}'),
   //   new Style('box-shadow: ${Shadow[5]}'),
   // ];
 
-  UINode content;
-  int level;
+  final UINode content;
+  final int level;
 
   UINode build() {
     // TODO(eseidel): Add a shadow.
     // return new StyleNode(content, _shadowStyle[level]);
     return content;
   }
 
 }