code: function () {
          var me = this,
              headerCt = me.view.headerCt;
          if (headerCt) {
              headerCt.items.each(function(header) {
                  var filter = me.getFilter(header.dataIndex);
                  header[filter && filter.active ? 'addCls' : 'removeCls'](me.filterCls);
              });
          }
      }
docs: Update the styles for the header row based on the active filters