Chrome Version: 67.0.3376.0/10505.0.0 dev-channel Daisy,Candy and Reks 
OS: Chrome

What steps will reproduce the problem?
(1)Recover build -> In Sign-in screen enter Email Id -> Now at Uber Tray turn-off WI-FI 
(2)Now "Network not available" page is seen ->observe unnecessary disabled 'Back' button is seen 
i.e. after connecting to network, automatically sign-in screen is seen but   'Back' button  will not be enabled,
(Please refer video)

Expected 'Back' button should not be available in "Network not available" page
Actual: Instead  unnecessary disabled 'Back' button is seen

This is Non-Regression Issue seen from M-66

@wzang : Please confirm the Issue
 

Deleted: Actual_UnnecessaryDisabledBackButton.mp4 18.6 MB

Actual_UnnecessaryDisabledBackButton.mp4 18.6 MB Download