AFAIK, we should be fine unifying the behaviour. What is the original reason we had this? Is it a bug or WAI ?

Rohit might be able to provide more background, it seems like a bug to not report on long-press. 

What do desktop and android do? We should just do exactly what they do and not come up with our own behavior. 

Good point, interestingly enough desktop and android do not report long press and window.history.go, so I will change the code to do the same:
https://cs.chromium.org/chromium/src/chrome/browser/ui/browser_commands.cc?q=%5C%22Back%5C%22&sq=package:chromium&l=391&dr=C

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d0b3868c2fee1da5c50b7b4d2d5c956835237b15

commit d0b3868c2fee1da5c50b7b4d2d5c956835237b15
Author: eugenebut <eugenebut@chromium.org>
Date: Tue Nov 08 23:29:24 2016

[ios] Unified CRWSessionController navigation logic.

Changed -[CRWSessionController goToEntry:] logic to do the same things
as goBack/goForward/goDelta: and made goDelta: call goToEntry:.

goToEntry: is used when user navigates to session entry by doing a long
press on back/forward button and picking an item from the dropdown, so
it should work exacly the same as if user directly tapped back or
forward.

This refactoring will also allow to unify CRWWebController's
goToItemAtIndex and goDelta.

BUG= 663072 

Review-Url: https://codereview.chromium.org/2485753002
Cr-Commit-Position: refs/heads/master@{#430756}

[modify] https://crrev.com/d0b3868c2fee1da5c50b7b4d2d5c956835237b15/ios/web/navigation/crw_session_controller.mm

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome/ios_internal.git/+/df749c8d9435be6787fe652b236deb10666b1dff

commit df749c8d9435be6787fe652b236deb10666b1dff
Author: eugenebut <eugenebut@google.com>
Date: Wed Nov 09 16:29:02 2016

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9f212096c8a1c0da4eea20c2069763fedd1a26b1

commit 9f212096c8a1c0da4eea20c2069763fedd1a26b1
Author: eugenebut <eugenebut@chromium.org>
Date: Wed Nov 09 16:30:26 2016

[ios] Removed User Action reporting from CRWSessionController.

User Action will be added to Tab code to match other platforms behavior:
Back and Forward actions are reported only when user taps Back or
Forward buttons; nothing is reported for HTML5 JS navigations and user
navigations initiated via long press and picking item from the dropdown.

BUG= 663072 

Review-Url: https://codereview.chromium.org/2476373004
Cr-Commit-Position: refs/heads/master@{#430948}

[modify] https://crrev.com/9f212096c8a1c0da4eea20c2069763fedd1a26b1/ios/web/navigation/crw_session_controller.mm

Verified in  56.0.2920.0 canary, iPhone 6S iOS 10.1, iPad mini4 iOS 10, 
"Back"/"Forward" actions looks good.