void Layer::commitChildList() {
    for (size_t i = 0; i < mCurrentChildren.size(); i++) {
        const auto& child = mCurrentChildren[i];
        child->commitChildList();
    }
    mDrawingChildren = mCurrentChildren;
    mDrawingParent = mCurrentParent;
}

• 拷贝 mCurrentChildren 到 mDrawingChildren。
• 拷贝 mCurrentParent 到 mDrawingParent。
• 递归 mCurrentChildren，执行上面两个操作。