Re-wire up the back button

sky/sdk/lib/widgets/navigator.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'basic.dart';
 
 typedef Widget Builder(Navigator navigator);
 
 abstract class RouteBase {
   RouteBase({ this.name });
@@ skipping 55 matching lines @@
     assert(historyIndex < history.length);
   }
 }
 
 class Navigator extends Component {
 
   Navigator(this.state, { String key }) : super(key: key);
 
   NavigationState state;
 
+  void syncFields(Navigator source) {
+    state = source.state;
+  }
+
   void pushNamed(String name) {
     setState(() {
       state.pushNamed(name);
     });
   }
 
   void push(RouteBase route) {
     setState(() {
       state.push(route);
     });
@@ skipping 14 matching lines @@
   void forward() {
     setState(() {
       state.forward();
     });
   }
 
   Widget build() {
     return state.currentRoute.build(this);
   }
 }