unsigned TileControllerMemoryHandler::totalUnparentedTiledLayers() const
{
    unsigned totalUnparentedLayers = 0;
    for (ListHashSet<TileController*>::const_iterator it = m_tileControllers.begin(); it != m_tileControllers.end(); ++it) {
        TileController* tileController = *it;
        totalUnparentedLayers += tileController->numberOfUnparentedTiles();
    }
    return totalUnparentedLayers;
}