anchor.diff:        [bool _skipLocationChange = false, bool _replaceState = false]) {
       return this._currentNavigation = this._currentNavigation.then((_) {
         this.lastNavigationAttempt = url;
  -      this._startNavigating();
  +      this._startNavigating(url);
         return this._afterPromiseFinishNavigating(
             this.recognize(url).then((instruction) {
           if (instruction == null) {
  
positive.code:   }
  
    /** @internal */
    void _startNavigating() {
      this.navigating = true;
    }
  
    /** @internal */
    void _finishNavigating() {
      this.navigating = false;
    }
  
    /// Subscribe to URL updates from the router
    Object subscribe(void onNext(dynamic value), [void onError(dynamic value)]) {
  
negative.code:       return _resolveToFalse;
      }
      return this._currentNavigation = this._currentNavigation.then((_) {
        this._startNavigating(instruction.toLinkUrl());
        return this._afterPromiseFinishNavigating(
            this._navigate(instruction, _skipLocationChange, _replaceState));
      });
  