def child_added(self, child):
        super(QtStackItem, self).child_added(child)
        if isinstance(child, QtContainer):
            self.widget.setStackWidget(self.stack_widget())
The ``Deferred`` returned by ``gather_deferreds`` does not fire until
dataset/ETHPy150Open ContinuumIO/ashiba/enaml/enaml/qt/qt_stack_item.py/QtStackItem.child_added--crossover with--dataset/ETHPy150Open ClusterHQ/flocker/flocker/common/test/test_defer.py/GatherDeferredsTests.test_fire_when_all_fired