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

sky/sdk/lib/framework/components2/modal_overlay.dart

Index: sky/sdk/lib/framework/components2/modal_overlay.dart
diff --git a/sky/sdk/lib/framework/components2/modal_overlay.dart b/sky/sdk/lib/framework/components2/modal_overlay.dart
index 282ee126c4a2ce102a9cb76e46d9165ebdccd059..34ff954c07856bed91390a7947df1f58defa4732 100644
--- a/sky/sdk/lib/framework/components2/modal_overlay.dart
+++ b/sky/sdk/lib/framework/components2/modal_overlay.dart
@@ -18,6 +18,12 @@ class ModalOverlay extends Component {
   List<UINode> children;
   GestureEventListener onDismiss;
 
+  void syncFields(ModalOverlay source) {
+    children = source.children;
+    onDismiss = source.onDismiss;
+    super.syncFields(source);
+  }
+
   UINode build() {
     return new EventListenerNode(
       new StackContainer(children: children),