anchor.diff:  import "dart:core";
   import "dart:uri";
   import "dart:html";
  -import 'package:web_ui/watcher.dart' as watchers;
   import 'package:web_ui/observe.dart';
   import 'package:delegate/delegate.dart';
   
  
positive.code: }
  
  class PageNavigator {
    final watch;
    final History history;
    final Router router;
    final Map<String, dynamic> views;
  
negative.code:   var activeWatchDisposer;
  
    PageNavigator(
      this.observe,
      this.history,
      this.router,
      this.views,
  