forked to ignore data-uri and put surrounded by url(data:image..)

CssRewriteUrlTransformIgnoringDataUri.cs

/// <remarks>Part of Microsoft.AspNet.Web.Optimization.1.1.3, forked to ignore data-uri</remarks>
/// <remarks>forked to ignore data-uri and put surrounded by url(data:image..)</remarks>
    /// <summary>
    /// Rewrites urls to be absolute so assets will still be found after bundling
    /// </summary>
    public class CssRewriteUrlTransformIgnoringDataUri : IItemTransform
    {
        internal static string RebaseUrlToAbsolute(string baseUrl, string url)
        {
            // Don't do anything to invalid urls or absolute urls or data:image urls
            if (String.IsNullOrWhiteSpace(url) ||
                String.IsNullOrWhiteSpace(baseUrl) ||
                url.StartsWith("data:image", StringComparison.CurrentCultureIgnoreCase) ||
                url.StartsWith("/", StringComparison.OrdinalIgnoreCase))
            {
                return url;
            }

            // NOTE: now we support for ~ app relative urls here
            if (!baseUrl.EndsWith("/", StringComparison.OrdinalIgnoreCase))
            {
                baseUrl += "/";
            }

            return VirtualPathUtility.ToAbsolute(baseUrl + url);
        }

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

            // Replace all urls with absolute urls
            var url = new Regex(@"url\(['""]?(?<url>[^)]+?)['""]?\)");
            return url.Replace(content, (match => 
                    "url(" + RebaseUrlToAbsolute(baseUrl, match.Groups["url"].Value) + ")")
                );
        }

        /// <summary>
        /// Converts any urls in the input to absolute using the base directory of the include virtual path.
        /// </summary>
        /// <param name="includedVirtualPath">The virtual path that was included in the bundle for this item that is being transformed</param>
        /// <param name="input"></param>
        /// <example>
        /// bundle.Include("~/content/some.css") will transform url(images/1.jpg) => url(/content/images/1.jpg)
        /// </example>
        public string Process(string includedVirtualPath, string input)
        {
            if (includedVirtualPath == null)
            {
                throw new ArgumentNullException("includedVirtualPath");
            }
            // Strip off the ~ that always occurs in app relative virtual paths
            string baseUrl = VirtualPathUtility.GetDirectory(includedVirtualPath.Substring(1));
            return ConvertUrlsToAbsolute(baseUrl, input);
        }
    }