Chrome Version: 62.0.3199.0/9892.0.0 dv-channel Daisy,Kip and Minnie
OS: Chrome

What steps will reproduce the problem?
(1)Open NTP >> Enable Chromevox >> Enter fullscreen mode and observe area near tabstrip
(2)Now hover on top and observe tabstrip

Expected:
After-1: No white patch should be seen.
After-2: On hovering no broken tabstrip should be seen.

Actual:
After-1: Unwanted white patch is seen on top of page when both fullscreen and chromevox are enabled
After-2: After hovering on top of page unwanted seperator line is seen below tabstrip and page.

This is a regression issue as same is working fine in M55.

Issue is not applicable to linux and windows