public function addSize($size, UrlContract $url)
    {
        $size = is_array($size) ? new Size($size[0], $size[1]) : $size;

        if ($size->equals($this->getSize())) {
            return $this;
        }

        $key = "$size";

        $this->sizes[$key] = $size;
        $this->sizeUrls[$key] = $url;

        return $this;
    }