anchor.diff:        filepath = path.join(options.outDir, _toSystemPath(id.path));
       } else {
         // TODO(sigmund): do something about other assets?
  -      continue;
  -    }
  -
  -    futures.add(_writeAsset(filepath, asset));
  -  }
  -  return Future.wait(futures);
  +      return null;
  +    }
  +
  +    return _writeAsset(filepath, asset);
  +  });
   }
   
   /**
  
positive.code: /** Copy a file from [inpath] to [outpath]. */
  Future _copyFile(String inpath, String outpath) {
    _ensureDir(path.dirname(outpath));
    var writer = new File(outpath).openWrite();
    return writer.addStream(new File(inpath).openRead())
        .then((_) => writer.close());
  }
  
  /** Write contents of an [asset] into a file at [filepath]. */
  Future _writeAsset(String filepath, Asset asset) {
    _ensureDir(path.dirname(filepath));
    var writer = new File(filepath).openWrite();
    return writer.addStream(asset.read()).then((_) => writer.close());
  }
  
negative.code:   _ensureDir(outPackages);
  
    // Copy all the files we didn't process
    var dirs = options.packageDirs;
  
    return Future.forEach(_polymerPackageDependencies, (package) {
      return Future.forEach(_listPackageDir(package, 'lib', options), (relpath) {
        var inpath = path.join(dirs[package], relpath);
        var outpath = path.join(outPackages, package, relpath.substring(4));
        return _copyFile(inpath, outpath);
      });
    });
  }
  
  /** Ensure [dirpath] exists. */
  