func (rt *Transport) WrappedRoundTripper() http.RoundTripper {
	return rt.RoundTripper
}

// rewriteURL rewrites a single URL to go through the proxy, if the URL refers
// to the same host as sourceURL, which is the page on which the target URL
// occurred, or if the URL matches the sourceRequestHost.
func (t *Transport) rewriteURL(url *url.URL, sourceURL *url.URL, sourceRequestHost string) string {
	// Example: