Used to handle key events on the QListView of the combobox.

def eventFilter(self, widget, event):
        """Used to handle key events on the QListView of the combobox."""
        if event.type() == QEvent.KeyPress and event.key() == Qt.Key_Delete:
            index = self.view().currentIndex().row()
            if index >= EXTERNAL_PATHS:
                # Remove item and update the view.
                self.removeItem(index)
                self.showPopup()
                # Set the view selection so that it doesn't bounce around.
                new_index = min(self.count() - 1, index)
                new_index = 0 if new_index < EXTERNAL_PATHS else new_index
                self.view().setCurrentIndex(self.model().index(new_index, 0))
                self.setCurrentIndex(new_index)
            return True
        return QComboBox.eventFilter(self, widget, event)