This has been known about for ages and was part of the Snowden leaks: https://www.google.com/search?q=google+nsa+%22encryption+add...
The parent poster was suggesting (and I was questioning) this occurred at Google Data Centers, which would prove explicit cooperation by Google.
A whole different ballgame.
The closest I've seen are the PRISM slides which imply cooperation from Google and the other big companies, but this could be bad choice of wording.
Regarding PRISM cooperation, I'm not sure where your doubt is coming from there. http://imgur.com/a/wRKtL
The slide was explicit, and is now many years out of date so without doubt the number of providers has increased. The means by which these provider agreements are reached is well known (National Security Letters) as is the fact that organizations are fully barred from disclosing their existence.