Google made HTTPS default-on in 2010, but there was a toggle so that you could disable the forced use:
* https://workspaceupdates.googleblog.com/2010/01/default-http...
In 2014 the toggle was removed and all connections were forced to HTTPS.
The Snowden revelations occurred in 2013:
Related: https://www.jefftk.com/p/history-of-https-usage
[1] https://googleblog.blogspot.com/2011/10/making-search-more-s...