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

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

Index: sky/sdk/lib/framework/components2/drawer_header.dart
diff --git a/sky/sdk/lib/framework/components2/drawer_header.dart b/sky/sdk/lib/framework/components2/drawer_header.dart
index 31dda11196dcab2b077f6ca91cebeb6803f169c9..dc43554ac9848719d062c9463a708bed4d6c8ffc 100644
--- a/sky/sdk/lib/framework/components2/drawer_header.dart
+++ b/sky/sdk/lib/framework/components2/drawer_header.dart
@@ -12,6 +12,11 @@ class DrawerHeader extends Component {
 
   List<UINode> children;
 
+  void syncFields(DrawerHeader source) {
+    children = source.children;
+    super.syncFields(source);
+  }
+
   UINode build() {
     return new Container(
       key: 'drawer-header-outside',