I wondered if Google's internal development infrastructure looks like or hooks into Google Code, making it easy to release code publicly on Google Code.

Not really... it's about the same amount of work whether it goes to Google Code or GitHub. The teams that have an easier time of it are those that are using Git+Gerrit internally, since a public release is as simple as `git remote add` and `git push`. A number of teams continue to use tools like https://code.google.com/p/make-open-easy/ with varying degrees of success.