static/ext/src/toolbar/Paging.js
function(){
        var me = this,
            last = me.getPageData().pageCount;

        if (me.fireEvent('beforechange', me, last) !== false) {
            me.store.loadPage(last);
        }
    }
function(){
        var me = this,
            last = me.getPageData().pageCount;

        if (me.fireEvent('beforechange', me, last) !== false) {
            me.store.loadPage(last);
        }
    }
Move to the last page, has the same effect as clicking the 'last' button.