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

sky/examples/stocks2/lib/stock_arrow.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/fn2.dart';
 import 'package:vector_math/vector_math.dart';
 import 'package:sky/framework/rendering/box.dart';
 import 'package:sky/framework/rendering/object.dart';
 import 'package:sky/framework/theme2/colors.dart' as colors;
 
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 
 class StockArrow extends Component {
-  double percentChange;
 
   StockArrow({ Object key, this.percentChange }) : super(key: key);
 
+  final double percentChange;
+
   int _colorIndexForPercentChange(double percentChange) {
     double maxPercent = 10.0;
     double normalizedPercentChange = math.min(percentChange.abs(), maxPercent) / maxPercent;
     return 100 + (normalizedPercentChange * 8.0).floor() * 100;
   }
 
   Color _colorForPercentChange(double percentChange) {
     if (percentChange > 0)
       return colors.Green[_colorIndexForPercentChange(percentChange)];
     return colors.Red[_colorIndexForPercentChange(percentChange)];
@@ skipping 35 matching lines @@
 
       canvas.restore();
     });
 
     return new Container(
         child: arrow,
         width: size,
         height: size,
         margin: const EdgeDims.symmetric(horizontal: 5.0));
   }
+
 }