Re-wire up the back button

sky/sdk/lib/widgets/navigator.dart

Index: sky/sdk/lib/widgets/navigator.dart
diff --git a/sky/sdk/lib/widgets/navigator.dart b/sky/sdk/lib/widgets/navigator.dart
index 74bf38077d98b1b381c9e6e2d6be77f6c3abb52a..3a6cad179874b1d5078649fecd86c794fb0bfb5d 100644
--- a/sky/sdk/lib/widgets/navigator.dart
+++ b/sky/sdk/lib/widgets/navigator.dart
@@ -73,6 +73,10 @@ class Navigator extends Component {
 
   NavigationState state;
 
+  void syncFields(Navigator source) {
+    state = source.state;
+  }
+
   void pushNamed(String name) {
     setState(() {
       state.pushNamed(name);