anchor.diff:   * --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() { 
  +void main() {
     Options options = new Options();
     var validArguments = ["--output_dir", "--dart2js_main"];
     var args = {};
  
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: import 'dart:io';
  
  Future<String> getVersion(var options, var rootPath) {
    var os = Platform.operatingSystem;
    var suffix = os == 'windows' ? '.exe' : '';
    var checkedInBinary =
        rootPath.join(new Path('tools/testing/bin/$os/dart$suffix'));
    var versionPath = rootPath.append("tools").append("version.dart");
    return Process.run(checkedInBinary.toNativePath(),
                       [versionPath.toNativePath()])
        .then((result) {
          if (result.exitCode != 0) {
  