bool WebGraphicsLayer::setChildren(const Vector<GraphicsLayer*>& children)
{
    bool ok = GraphicsLayer::setChildren(children);
    if (!ok)
        return false;
    for (int i = 0; i < children.size(); ++i) {
        WebGraphicsLayer* child = toWebGraphicsLayer(children[i]);
        child->setContentsScale(m_contentsScale);
        child->notifyChange();
    }
    notifyChange();
    return true;
}
void WebGraphicsLayer::setMaskLayer(GraphicsLayer* layer)
{
    if (layer == maskLayer())
        return;

    GraphicsLayer::setMaskLayer(layer);

    if (!layer)
        return;

    layer->setSize(size());
    WebGraphicsLayer* webGraphicsLayer = toWebGraphicsLayer(layer);
    webGraphicsLayer->setLayerTreeTileClient(layerTreeTileClient());
    webGraphicsLayer->setMaskTarget(this);
    webGraphicsLayer->setContentsScale(m_contentsScale);
    webGraphicsLayer->notifyChange();
    notifyChange();

}