This is actually present on all devices, and for all of the popups. A more general repro step:

- Long-press to show any pop-up menu (navigation, search accelerator, tab switcher). 
- Drag to scroll in the menu. At least one menu item's worth of space can be exposed above and below the content, even if all of the menu items fit in the initial menu bounds.

Keeping as P2.

pmadalla@: I am not able to reproduce.
There is the behavior describe in #1, which is WAI. This allows you to overscroll the popup menus, but the items should go back to their place. However in your video, the item isn't going back and the blank screen is still displayed even after releasing the scroll.

I tried reproducing on iPad pro 10.5, iOS 12 and iPad Air iOS 11.3 but I failed. Are you still able to do it? Do you have any other flag enabled?

I can reproduce issue in iPad (iOS 10.3.3) works fine in iPad(iOS 11.4 & iOS 12).
tested on the build version 69.0.3497.15 beta

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6a519c561be7b2bd29b53a26a9e63e81e288cb97

commit 6a519c561be7b2bd29b53a26a9e63e81e288cb97
Author: Gauthier Ambard <gambard@chromium.org>
Date: Wed Aug 08 10:05:09 2018

Remove inset at the bottom of the popup menus

The popup menus have a bottom inset because of the style of the table
view used. This CL prevents its by adding a dummy footer and settings
the footer height to 0.
This only happened on iOS 10.

Bug:  867782 
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Ia05e0a94f136e1cfaffb9e67bbc1bd09c606a5b2
Reviewed-on: https://chromium-review.googlesource.com/1166905
Reviewed-by: Stepan Khapugin <stkhapugin@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581510}
[modify] https://crrev.com/6a519c561be7b2bd29b53a26a9e63e81e288cb97/ios/chrome/browser/ui/popup_menu/popup_menu_table_view_controller.mm

Verified in:

App Version: 70.0.3521.0 canary
Devices: iPadMini
iOS Version: 10.3.3

No extra space is visible below popup menu items. Issue is fixed.