Override this function to apply custom CSS classes to rows during rendering. This function should return the CSS class name (or empty string '' for none) that will be added to the row's wrapping div. To apply multiple class names, simply return them space-delimited within the string (e.g. 'my-class another-class'). Example usage:

viewConfig: {
    getRowClass: function(record, rowIndex, rowParams, store){
        return record.get("valid") ? "row-valid" : "row-error";
    }
}