January 2017 - last edited January 2017
That is all I found:
1. Official requirements: https://support.google.com/analytics/answer/2700409?hl=en
2. First article about that: https://webgilde.com/en/analytics-opt-out/
3. It helps to generate your policy: http://www.iubenda.com/blog/privacy-policy-google-analytics/
4. Information about European laws: https://www.cookiechoices.org/
Hope this helps.