static/ext/src/selection/Model.js
function(record) {
        record = Ext.isNumber(record) ? this.store.getAt(record) : record;
        return this.selected.contains(record);
    }
function(record) {
        record = Ext.isNumber(record) ? this.store.getAt(record) : record;
        return this.selected.contains(record);
    }
Returns true if the specified row is selected.
@param {Ext.data.Model/Number} record The record or index of the record to check
@return {Boolean}