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

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

Index: sky/sdk/lib/framework/components2/button.dart
diff --git a/sky/sdk/lib/framework/components2/button.dart b/sky/sdk/lib/framework/components2/button.dart
index 6a743b2c3cda943a44b1b865ee7d160419fd27b0..858a709fd2d29114ed666c9001c527b1859d1068 100644
--- a/sky/sdk/lib/framework/components2/button.dart
+++ b/sky/sdk/lib/framework/components2/button.dart
@@ -22,6 +22,12 @@ class Button extends Component {
   UINode content;
   int level;
 
+  void syncFields(Component source) {
+    content = source.content;
+    level = source.level;
+    super.syncFields(source);
+  }
+
   UINode build() {
     return new StyleNode(
       new Material(