This is a Google Code post-receive hook that will automatically close review requests as "submitted" after a push. To determine which review requests should be closed, it scans through each commit's commit message for the following strings (case-insensitive): "Reviewed at <reviewboard_url>/r/<id>" or "Review request #<id>".
This is what the JSON payload looks like:

http://code.google.com/p/support/wiki/PostCommitWebHooks

All tests performed using an SVN and Mercurial repositories.
1) Push with the review request id in the commit message. Review request closed. [PASSED]

2) Push without a review request id in the commit message. (Error: Review request does not exist) [PASSED].

3) Push with non existent review request id. (Error: Review request does not exist) [PASSED]

4) Push with review id in the message that is already submitted. (logged a warning: request id already submitted.) [PASSED]

5) Push with review id in the message that has been marked as discarded. (review request marked as submitted.) [PASSED]