Review app and underlying platform change that support MMS.

Large complex feature, large attack surface ->P1

Reviewed MMS app inside gaia SMS app, and a high level review of MMS gecko code. The main control for MMS,as with SMS is that it is protected by the 'sms' permission, which is certified only. Gaia Components: One potential issue was identified relating to MMS. See 912885 for details. Other notes rolled into SMS gaia review: https://wiki.mozilla.org/Security/Reviews/Gaia/sms Gecko Components: - Re-uses existing system messages (sms-sent, sms-recieved) which have permission checks on them - Only content accessible interface (apart from readonly) is under navigator, and requires 'sms' permission - Examined code to look for any risk of malformed MMS causing issues. Most parsing happens at Gaia layer though. Would be good to fuzz MMS (in a similar manner to existing SMS fuzzing). I'll raise a separate bug for this testing.

(In reply to Paul Theriault [:pauljt] from comment #2) > Gaia Components: > One potential issue was identified relating to MMS. See 912885 for details. Note that I still have a sec-approval request there ;)