code: private JsCodeBuilder changeIndentHelper(int chg) {
      int newIndentDepth = indent.length() + chg * INDENT_SIZE;
      Preconditions.checkState(newIndentDepth >= 0);
      indent = Strings.repeat(" ", newIndentDepth);
      return this;
    }
docs: Helper for the various indent methods.
  @param chg The number of indent levels to change.