I was wondering about that case. Here's the next edit, which I think is closer to what you want (the data: acceptance is not in yet, this is just bypassing the original_url test and clearer error message):

	var validSchemes = {'https': 1, 'data': 1}; // 'app'?
        if (paramsFromRP.siteLogo) {
          // Regularize URL; throws error if input is relative.
          params.siteLogo = fixupURL(origin_url, paramsFromRP.siteLogo);
          /*jshint newcap:false*/
          if (!(URLParse(params.siteLogo).scheme in validSchemes)) {
            throw new Error("siteLogos can only be served from " + _.keys(validSchemes) + " schemes.");
          }
        }