Chrome Version: 62.0.3202.31/9901.29.0 dev-channel Daisy,Reks and Candy
OS: Chrome

What steps will reproduce the problem?
(1)Sign in to user -> Go to chrome://settings/accounts page
(2)In 'Manage Other users' page -> Enable  'Restrict sign-in to the following users' option so that 'Add person' option is enabled
(3)Now click on 'Add person' -> Enter any email id (Ex: msatlinux)
(4)Now click on 'Add person' and again add same email id (msatlinux) and click on 'ADD' -> observe 'Add person' Dialog box closes as it is allowing to add that person (Please refer Video)

Expected: When adding same email id (For Ex: msatlinux) 'Add person' Dialog box should not close i.e. Error message such as 'Already person is added' should be seen 

Actual: Instead Error message is not seen while adding same person and 'Add person' Dialog box closes  

Note: 
1.But in added person list Duplicate Email Ids are not seen
2.Issue is seen on latest M-63 also

This is Regression issue as same is working fine in old chrome://settings page i.e. not allowing to add same person

@stevenjb : Please confirm the Issue
 

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