code: private JsMessage getTrackedMessage(NodeTraversal t, String msgName) {
      boolean isUnnamedMessage = isUnnamedMessageName(msgName);
      if (!isUnnamedMessage) {
        MessageLocation location = messageNames.get(msgName);
        return location == null ? null : location.message;
      } else {
        Var var = t.getScope().getVar(msgName);
        if (var != null) {
          return unnamedMessages.get(var);
        }
      }
      return null;
    }
docs: Get a previously tracked message.