https://gerrit.wikimedia.org/robots.txt : gerrit is currently well crawled, e.g. https://www.google.it/search?q=site%3Agerrit.wikimedia.org .
It seems most instances don't allow crawling of the code review portion, would need to confirm it is possible.
https://secure.phabricator.com/robots.txt
https://developer.blender.org/robots.txt
http://reviews.llvm.org/robots.txt