You may be thinking of PageSpeed Service[0], which was a proxy service of Google's. PageSpeed Service was shut down[3] in May of 2015. PageSpeed Insights[1] is a service of theirs that checks pages for usability and performance and is still active. There is also a PageSpeed Insights SDK[2] available, so you could self-host if they decide to stop offering the service.

[0] https://developers.google.com/speed/pagespeed/service

[1] https://developers.google.com/speed/pagespeed/insights/

[2] https://code.google.com/p/page-speed/

[3] http://techcrunch.com/2015/05/06/google-shuts-down-pagespeed...