anchor.diff:     * If the given URL does not begin with `/`, the router will navigate relative to this component.
      */
     Future<dynamic> navigateByUrl(String url,
  -      [bool _skipLocationChange = false]) {
  +      [bool _skipLocationChange = false, bool _replaceState = false]) {
       return this._currentNavigation = this._currentNavigation.then((_) {
         this.lastNavigationAttempt = url;
         this._startNavigating();
  
positive.code:     var promise = super.commit(instruction);
      if (!_skipLocationChange) {
        promise = promise.then((_) {
          this._location.go(emitPath, emitQuery);
        });
      }
      return promise;
  
negative.code:       }
        return this._routerCanDeactivate(instruction).then((bool result) {
          if (result) {
            return this
                .commit(instruction, _skipLocationChange, _replaceState)
                .then((_) {
              this._emitNavigationFinish(instruction.rootUrl);
              return true;
            });
  