lib/Ext/navigation/View.js
function(toolbar, item) {
        item.un({
            scope: this,
            show: this.refreshBackButtonContainer,
            hide: this.refreshBackButtonContainer
        });
        this.refreshBackButtonContainer();
    }
function(toolbar, item) {
        item.un({
            scope: this,
            show: this.refreshBackButtonContainer,
            hide: this.refreshBackButtonContainer
        });
        this.refreshBackButtonContainer();
    }
This is called when an Item is removed from the BackButtonContainer of a SplitNavigation View
@private

@param toolbar
@param item