anchor.diff:  
       _optionsListener?.cancel();
       _optionsListener = options?.stream?.listen((_) {
  +      _changeDetector.markForCheck();
         _updateActiveModel();
         _setInitialActiveItem();
       });
  
positive.code: 
    String _ariaActiveDescendant;
  
    MaterialDropdownSelectComponent(
        @Optional() IdGenerator idGenerator,
        @Optional() @SkipSelf() this._popupSizeDelegate,
        @Optional() @Inject(rtlToken) bool rtl,
        @Attribute('popupClass') String popupClass,
        @Attribute('buttonAriaRole') this.buttonAriaRole,
        HtmlElement element)
        : activeModel = ActiveItemModel(idGenerator),
          popupClassName = constructEncapsulatedCss(popupClass, element.classes),
  
negative.code: 
    @override
    set selection(SelectionModel<T> newSelection) {
      _changeDetector.markForCheck();
      super.selection = newSelection;
      _setInitialActiveItem();
  
      _selectionListener?.cancel();
      _selectionListener = selection?.selectionChanges?.listen((changes) {
        _changeDetector.markForCheck();
        // Update active item if new items are selected.
        var added =
            changes.last.added.isNotEmpty ? changes.last.added.first : null;
  