anchor.diff:  }
   
   JSCode jsProgramToCode(JS.Program moduleTree, ModuleFormat format,
  -    {bool buildSourceMap: false, String jsUrl, String mapUrl}) {
  +    {bool buildSourceMap: false,
  +    String jsUrl,
  +    String mapUrl,
  +    String customScheme}) {
     var opts = new JS.JavaScriptPrintingOptions(
         allowKeywordsInProperties: true, allowSingleLineIfStatements: true);
     var printer;
  
positive.code: 
    Map builtMap;
    if (buildSourceMap && sourceMap != null) {
      builtMap =
          placeSourceMap(sourceMap.build(jsUrl), mapUrl, <String, String>{});
      var jsDir = path.dirname(path.fromUri(jsUrl));
      var relative = path.relative(path.fromUri(mapUrl), from: jsDir);
      var relativeMapUrl = path.toUri(relative).toString();
  
negative.code:   var jsCode = jsProgramToCode(jsModule, moduleFormat,
        buildSourceMap: argResults['source-map'],
        jsUrl: path.toUri(output).toString(),
        mapUrl: path.toUri(output + '.map').toString(),
        customScheme: customScheme);
    file.writeAsStringSync(jsCode.code);
  
    if (jsCode.sourceMap != null) {
  