>>107592586
>>107592941
>>107592951
It is bound, but there's a small typo in info.el. On line 4234
(define-key map [tool-bar C-Back\ in\ history] 'Info-history-back-menu)
"history" in the key sequence is uncapitalized, but as you can see in >>107591233 it should be capitalized. So the fix is
(define-key Info-mode-map [tool-bar C-Back\ in\ History] 'Info-history-back-menu)
idem for the forward-menu command. Someone should send a bugfix.