anchor.diff:    if (!args.containsKey("output_dir")) throw "Please specify output_dir";
   
     var scriptFile = new File(options.script);
  -  var path = new Path(scriptFile.directorySync().path); 
  +  var path = new Path(scriptFile.directorySync().path);
     var rootPath = path.directoryPath.directoryPath;
   
     getSnapshotGenerationFile(options, args, rootPath).then((result) {
  
positive.code:  * --output_dir=val     The full path to the output_dir.
   * --dart2js_main=val   The path to the dart2js main script releative to root.
   */
  void main() { 
    Options options = new Options();
    var validArguments = ["--output_dir", "--dart2js_main"];
    var args = {};
  
negative.code:   var dart2js = rootPath.append(args["dart2js_main"]);
  
    return getVersion(options, rootPath).then((version) {
      var snapshotGenerationText =
  """
  import '${dart2js}' as dart2jsMain;
  import 'dart:io';
  