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

sky/examples/stocks2/lib/stock_menu.dart

Index: sky/examples/stocks2/lib/stock_menu.dart
diff --git a/sky/examples/stocks2/lib/stock_menu.dart b/sky/examples/stocks2/lib/stock_menu.dart
index c4e261d34c59084be28b0805e9892d245a416f28..67fb165d77ff037a710289994d8bc6ec9ea1beb0 100644
--- a/sky/examples/stocks2/lib/stock_menu.dart
+++ b/sky/examples/stocks2/lib/stock_menu.dart
@@ -8,12 +8,19 @@ import 'package:sky/framework/components2/checkbox.dart';
 import 'package:sky/framework/theme/view_configuration.dart';
 
 class StockMenu extends Component {
-  PopupMenuController controller;
 
   StockMenu({Object key, this.controller, this.autorefresh: false, this.onAutorefreshChanged}) : super(key: key);
 
-  final bool autorefresh;
-  final ValueChanged onAutorefreshChanged;
+  PopupMenuController controller;
+  bool autorefresh;
+  ValueChanged onAutorefreshChanged;
+
+  void syncFields(StockMenu source) {
+    controller = source.controller;
+    autorefresh = source.autorefresh;
+    onAutorefreshChanged = source.onAutorefreshChanged;
+    super.syncFields(source);
+  }
 
   UINode build() {
     var checkbox = new Checkbox(