code: static void cannotConvertYet(AbstractCompiler compiler, Node n, String feature) {
      compiler.report(JSError.make(n, CANNOT_CONVERT_YET, feature));
    }
docs: Warns the user that the given ES6 feature cannot be converted to ES3
  because the transpilation is not yet implemented. A call to this method
  is essentially a "TODO(tbreisacher): Implement {@code feature}" comment.