Thanks for your report. I don't see those on my 68.0.3406.0 instance O_o. I'll have a look into what's going on there. They are supposed to never show on Mac.

I'm glad I took the screenshot - I can't reproduce it this morning. Makes me suspect it happened after a particular sequence of events. I will keep an eye out for that.

I figured out how to repro this: have keyboard focus on the app button and hit space to open the menu.

https://chromium-review.googlesource.com/c/chromium/src/+/1050068

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cbc70bf500172632ab61df8122c0b15a91e6edef

commit cbc70bf500172632ab61df8122c0b15a91e6edef
Author: Elly Fong-Jones <ellyjones@chromium.org>
Date: Tue May 08 21:33:00 2018

macviews: disable menu mnemonics

These aren't used in Mac apps. They aren't *shown* in MacViews, but they were
still used, which meant that trying to prefix search could instead activate
an item by mnemonic.

Test: Manual
1) Open the app menu
2) Press "N"
Before this CL, "New Window" is activated; after it, "New Tab" is
prefix-selected.

Bug:  836964 
Change-Id: Id672a1e17589e3ebd09e6bff473341947bd2df2a
Reviewed-on: https://chromium-review.googlesource.com/1050305
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556966}
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/chrome/browser/ui/views/menu_controller_interactive_uitest.cc
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/ui/views/controls/menu/menu_config.cc
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/ui/views/controls/menu/menu_config.h
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/ui/views/controls/menu/menu_config_mac.mm
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/ui/views/controls/menu/menu_item_view.cc
[modify] https://crrev.com/cbc70bf500172632ab61df8122c0b15a91e6edef/ui/views/controls/menu/menu_item_view_unittest.cc

Can this be marked as fixed if nothing else is pending?

There's one more part to the fix pending: <https://chromium-review.googlesource.com/c/chromium/src/+/1050068>.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6ad1ebefd9f6d130b822eff6e9c66847042c419f

commit 6ad1ebefd9f6d130b822eff6e9c66847042c419f
Author: Elly Fong-Jones <ellyjones@chromium.org>
Date: Mon May 14 14:44:17 2018

macviews: never show mnemonics

Even when the parent MenuButton has keyboard focus, mnemonics should never
show on Mac.

Bug:  836964 
Change-Id: If3906f664387c2730bc18f2c2bf638de6025c597
Reviewed-on: https://chromium-review.googlesource.com/1050068
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558300}
[modify] https://crrev.com/6ad1ebefd9f6d130b822eff6e9c66847042c419f/ui/views/controls/menu/menu_runner_impl.cc

Able to reproduce the issue on Mac 10.13.3 using chrome reported version #68.0.3406.0

Verified the fix on Mac 10.13.3 using Chrome version #68.0.3431.0 as per the comment #7.
Attaching screen cast for reference.
Observed that on opening the app menu and pressing "N", focussed on "New Tab" in the menu rather than opening a new window. 
Hence, the fix is working as expected. 
Adding the verified labels.

Thanks...!!

Deleted: 836964.mp4 508 KB

	836964.mp4 508 KB View Download