Where did advanced-cache.php come from?

I’ve been having some site slow down issues, and in snooping through my directories, under wp-content I located advanced-cache.php, with time stamp of 5/23/13. I haven’t installed any caching plugins (this one shows as a drop-in in my plugins page) other than W3TC, and the latest update for that was 5/25/13. Can anyone give me a clue how advanced-cache.php got there? Did it come with the latest W3TC?