UserAgent: Mozilla/5.0 (X11; CrOS x86_64 8872.73.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.103 Safari/537.36

Steps to reproduce the problem:
1. Supervised user unable to add extension 
2. No option in supervised user management page to add extension
3. 

What is the expected behavior?
Add adBlocking extension to children's account

What went wrong?
Can't add adblocking extension to children's user account. I bought a chromebook specifically because I thought it would give me the best control but he's seeing all sorts of ads because I'm unable to add the adblocking extension to his account.

WebStore page: Adblock

Did this work before? No 

Chrome version: 55.0.2883.103  Channel: stable
OS Version: 8872.73.0
Flash Version: Shockwave Flash 24.0 r0

I bought a chromebook specifically because I thought it would give me the best control but he's seeing all sorts of ads because I'm unable to add the adblocking extension to his account.

Please fix ASAP or stop advertising it as good for children.