anchor.diff:    var activeWatchDisposer;
   
     PageNavigator(
  -    this.watch,
  +    this.observe,
       this.history,
       this.router,
       this.views,
  
positive.code:       this.activeWatchDisposer();
      }
  
      this.activeWatchDisposer = this.watch(match[1], (e) {
        this.history.replaceState(null, null,
          this.router.routePath(this.activeRoute, e.newValue)
        );
      });
  
negative.code: import "dart:core";
  import "dart:uri";
  import "dart:html";
  import 'package:web_ui/observe.dart';
  import 'package:delegate/delegate.dart';
  
  