Version: 52.0.2729.0 
OS: Ubuntu 12.04,14.04,Windows

Precondition: 
1.Enable 'Material Design User Manager' flag from 'chrome://flags'
2.Make sure that there are 9 or more supervised Users

What steps will reproduce the problem?
(1)Launch chrome -> Sign into Profile-> click on avatar icon 
(2)Now click on 'Switch person' option for User Manager window-> Select 'ADD PERSON' -> Now Check the 'Supervise this person...' checkbox ->Select account 
(3)Now click on "Import an existing supervised user" link and observe overlay(Please refer "Actual_Overlay" Video)

Expected:  Scrollbar should be seen in "Import an existing supervised user"  Overlay if there are more supervised Users 
Actual: Instead Buttons are seen missing and it is difficult to cancel or import the Users 

This is Non-Regression Issue as "Import an existing supervised user" link is available from 52.0.2716.0 

Note:
1.In Chrome://Settings page On clicking "Import an existing supervised user" link scrollbar is seen i.e. able to import or cancel (Please refer "Expected_Overlay" Video)

2. Same Issue is seen on clicking "import.." link which is available at Alert Message(Please refer Video)

Below is the MANUAL CHANGELOG URL:
https://chromium.googlesource.com/chromium/src/+log/52.0.2715.0..52.0.2716.0?pretty=fuller&n=10000

Suspecting https://codereview.chromium.org/1901853002 from Manual Changelog

@mahmadi : Please feel free to re-assign if its not related to your change
 

Deleted: Actual_Overlay.ogv 2.7 MB

Actual_Overlay.ogv 2.7 MB Download

Deleted: Expected_Overlay.ogv 1.5 MB

Expected_Overlay.ogv 1.5 MB Download