please:
* put the "classList" or the "parentNode" object in a variable, so that you can reuse it. For example: "lineNode" or "lineClassList"
* take care that the line is not too long
* please augment the unit tests in https://github.com/mozilla-b2g/gaia/blob/master/apps/sms/test/unit/thread_ui_test.js#L2990-L3088, you'll need to add an error incoming message and try to click on it