If you meant to unsubscribe -
Try sending a blank e-mail to
chromium-app...@chromium.org (note that +unsubscribe in the address, it is important). It should not be in the body or subject of the message, it should be the recipient.
If that does not work and you are still getting e-mails -
1. Go to http://groups.google.com/a/chromium.org/group/chromium-apps/subscribe?hl=en.
2. You might need to log in. If you do -
2a. Click on the "Enter your email address to access the document" link, at the bottom of the "Sign in to your account at Chromium.org" box.
2b. Type your e-mail there and press Enter.
2c. Log in regularly, if it asks you to.
3. Click on "Unsubscribe".