• Go to the settings menu, and scroll down to “About phone.” Tap it.
• Scroll down to the bottom again, where you see “Build number.” (Your build number may vary from ours here.)
• Tap it seven (7) times. After the third tap, you'll see a playful dialog that says you're four taps away from being a developer. (If only it were that simple, eh?) Keep on tapping, and *poof*, you've got the developer settings back.

Warning /!\ Warning: Disconnect ALL other mobile devices connected from your computer or they might get erased too. This will erase ALL DATA on your Nexus 7. Warning /!\

In case anything happens while developing, the system image for Nexus 7 can be found here: https://dl.google.com/dl/android/aosp/nakasi-jdq39-factory-c317339e.tgz

Please also check for updated Nexus7 (nakasi) factory images as well.

After downloading the above tarball, uncompress it with the following:

tar zxvf nakasi-jdq39-factory-c317339e.tgz

Then, place your machine into fastboot mode and run the resulting script:

cd nakasi-jdq39/
sudo ./flash-all.sh

You may get the following warnings, which you can ignore, the restoration will continue anyway.

archive does not contain 'boot.sig'
archive does not contain 'recovery.sig'
archive does not contain 'system.sig'

Then you may lock the device again after another reboot into the fastboot mode:

sudo fastboot oem lock