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