ChromeOS version: 70.0.3538.110 https://drive.google.com/open?id=1lXSh6VplUhUiRL1pYI8gv-Y-h77L9hx5
ChromeOS device model: ASUS Chromebox CN62
Case#: 17580953

Description: on the first login on a chromebox with two monitor it's enabled by policy the UnifiedDesktop when you disable the UnifiedDesktop and enable the mirror mode, you can't re-enable the UnifiedDesktop after disabling the mirror mode


Steps to reproduce: 
1) Have 2 displays connected. 
1a) if the user has already logged in go to Chrome://flags – enable(restart) disable(restart) unified desktop to reset
2) push the policy UnifiedDesktopEnabledByDefault (the customer is doing the same)
3) go to "Settings>Device>Displays" and disable unified
4) go to "Settings>Device>Displays" and enable mirror mode 
5) Confirm displays are mirrored. 
6) go to "Settings>Device>Displays" and disable mirror mode. 


Current Behavior / Reproduction: 
7) go to "Settings>Device>Displays" and see that the unified button is not there anymore: https://drive.google.com/open?id=1XWVsrndo22ocbWq35cCSrZ_ptQJMpQ6A
my repro: https://drive.google.com/open?id=1_AknjuxsVu7Tl-2gQEzRlExVoXiFaUBU
customer repro: https://drive.google.com/open?id=1skuneOAXMWCyidn1xskn9gIFW57uKM0L

Expected Behavior: 
being able to enable again the unified desktop
Drive link to logs: 
my debug_logs: https://drive.google.com/open?id=15L08U-XisyCwe2lg9W_eix-F-m_gx96P
customer debug_logs: https://drive.google.com/open?id=1LeGWVCs3XeXb1-Z3ICLT6rLP4O7mXHy5
policy: 
json: https://drive.google.com/open?id=1jfEEsX0-7uAiwNjcjgCYwI3uHFhycpo2
pdf: https://drive.google.com/open?id=1zsDAXYiReimR_O81ZH-i3H_j6PMfjh0u

Workaround:
keep the flag chrome://flags/#ash-enable-unified-desktop on