Comment #22 on issue 333062 by
abcarius...@student.sanjuan.edu: Two-sided
printing option missing in print dialog
https://code.google.com/p/chromium/issues/detail?id=333062
I had this exact problem and here how i fixed it:
1. Go to "Control Panel\Hardware and Sound\Devices and Printers"
2. Click on the printer you're trying to "Duplex print" from
3. Click on "Customize your printer".
4. Click "Change Properties".
5. Navigate to the "Device Settings" tab.
6. Under "Installable Optins", make sure that "Duplex Unit" is set
to "Installed". It should look like this "---Duplex Unit: Installed".
7. Now press "Apply" and it should be working.