CssRewriteUrlTransform data URI workaround

CssRewriteUrlTransformIgnoringDataUri.cs

/// <remarks>Part of Microsoft.AspNet.Web.Optimization.1.1.3, forked to ignore data-uri</remarks>
    public class CssRewriteUrlTransformIgnoringDataUri : IItemTransform
    {
        internal static string RebaseUrlToAbsolute(string baseUrl, string url)
        {
            if (string.IsNullOrWhiteSpace(url) || string.IsNullOrWhiteSpace(baseUrl) || url.StartsWith("/", StringComparison.OrdinalIgnoreCase))
                return url;
            if (!baseUrl.EndsWith("/", StringComparison.OrdinalIgnoreCase))
                baseUrl = baseUrl + "/";
            return VirtualPathUtility.ToAbsolute(baseUrl + url);
        }

        internal static string ConvertUrlsToAbsolute(string baseUrl, string content)
        {
            if (string.IsNullOrWhiteSpace(content))
            { return content; }

            return new Regex("url\\(['\"]?(?<url>[^)]+?)['\"]?\\)").Replace(content, match =>
            {
                var format = match.Groups["url"].Value;
                if (format.StartsWith("data:image", StringComparison.CurrentCultureIgnoreCase))
                {
                    return format;
                }

                return "url(" + RebaseUrlToAbsolute(baseUrl, format) + ")";
            });
        }

        public string Process(string includedVirtualPath, string input)
        {
            if (includedVirtualPath == null)
            {
                throw new ArgumentNullException("includedVirtualPath");
            }
            return ConvertUrlsToAbsolute(VirtualPathUtility.GetDirectory(includedVirtualPath.Substring(1)), input);
        }
    }

look at
https://github.com/benmccallum/AspNetBundling/blob/master/AspNetBundling/CssRewriteUrlTransformFixed.cs