code: private StringInfo getOrCreateStringInfo(String string) {
      StringInfo info = stringInfoMap.get(string);
      if (info == null) {
        info = new StringInfo(stringInfoMap.size());
        stringInfoMap.put(string, info);
      }
      return info;
    }
docs: Looks up the {@link StringInfo} object for a JavaScript string. Creates
  it if necessary.