anchor.diff:          MaterialButtonWrapper,
           TrackLayoutChangesMixin,
           KeyboardHandlerMixin,
  -        ActivateItemOnKeyPressMixin,
  +        ActivateItemOnKeyPressMixin<T>,
           ShiftClickSelectionMixin<T>
       implements PopupSizeProvider, OnChanges, OnDestroy {
     /// Function for use by NgFor for optionGroup.
  
positive.code: 
  // TODO(google): Move it to a common home to increase reusability.
  // TODO(google): Better comparison of characters to better support i18n.
  class ActivateItemOnKeyPressMixin {
    static Map<int, String> _charCodeMap = <int, String>{};
  
    String _enteredKeys = '';
  
negative.code:       ActiveItemModel activeModel,
        int charCode,
        SelectionOptions options,
        ItemRenderer<T> itemRenderer,
        SelectionModel selection) {
      // Guard against being called when not all data is initialized.
      if (itemRenderer == null || options == null) return;
  