UserAgent: Mozilla/5.0 (X11; CrOS x86_64 8172.47.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36
Platform: 8172.47.0 (Official Build) stable-channel stout

Steps to reproduce the problem:
1. Admin console: move managed Chromebook to designated OU
2. In Chrome Mngmnt/Device Settings: set Public session
3. in Chrome Mngmnt/Public Session settings: select Chrome Extension to "force install", eg. Google Cast
4. On Chromebook, check policy ExtensionInstallForcelist -- extension ID is listed.

What is the expected behavior?
On the managed Chromebook, in a Public Session, the Google Cast extension would be added.

What went wrong?
Google Cast extension never shows up.

Tested several other extensions with similar results.

Support pages are not clear as to which Extensions are allowed in Public Sessions.

Further, there is no whitelist capability in the Admin console / Chrome Management settings for Public Sessions Extensions.

Did this work before? No 

Chrome version: 51.0.2704.79  Channel: stable
OS Version: 8172.47.0
Flash Version: Shockwave Flash 21.0 r0