Version: 51.0.2704.81 official build
OS: Android 6.0.1

What steps will reproduce the problem?
(1) open a tab viewing google.com
(2) open another tab viewing gmail.com
(3) close the 2nd tab gmail.com
(4) press ctrl-shift-t

What is the expected output?
the last closed tab being undo.

What do you see instead?
nothing