code: function(view, initial){
          var me = this,
              checkbox = me.injectCheckbox,
              headerCt = view.headerCt;
  
          // Preserve behaviour of false, but not clear why that would ever be done.
          if (checkbox !== false) {
              if (checkbox == 'first') {
                  checkbox = 0;
              } else if (checkbox == 'last') {
                  checkbox = headerCt.getColumnCount();
              }
              Ext.suspendLayouts();
              if (view.getStore().buffered) {
                  me.showHeaderCheckbox = false;
              }
              headerCt.add(checkbox,  me.getHeaderConfig());
              Ext.resumeLayouts();
          }
  
          if (initial !== true) {
              view.refresh();
          }
      }
docs: Add the header checkbox to the header row
  @private
  @param {Boolean} initial True if we're binding for the first time.