GeoExt 2 /PrintExtent

Question

I would like to add an extent polygon here in this example:http://geoext.github.com/geoext2/examples/printextent/print-extent.html to may panel, not generating a new one. here is my map initialization :

Ext.define('MyApp.Map', {
        extend: 'GeoExt.panel.Map',
        alias: 'widget.mymap',

        initComponent: function () {  
         var me = this;

            Ext.apply(me, {
                map: map,
            });

        me.callParent(arguments);
    }
});

then add map to mapPanel

Ext.getCmp('mapPanel').add({requires: ['MyApp.Map'], items: [{xtype: 'mymap'  }] });

but I am stuck trying to add that plugin to my panel. In the example it seems simple but I couldn't do it! I am not sure where I have to add the plugin in my case.