+owen +evan 
Yes please remove the contextual menu on CrOS. 
Please make sure this doesn't affect other platform unless they also want it.
I know there was a bug around that issue but I can't seem to find it. 

Peter, Own, Evan, feel free to chime in.

IIRC everyone is happy with removing only on Chrome OS.

https://crrev.com/c/844048

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3090b8bbebb702a4f7c823a8141a4107919bc17c

commit 3090b8bbebb702a4f7c823a8141a4107919bc17c
Author: Tetsui Ohkubo <tetsui@chromium.org>
Date: Fri Jan 12 02:23:11 2018

Remove notification right click menu from Chrome OS.

This CL removes the right click menu of notification from Chrome OS.
As inline setting is added to Notification on Chrome OS, right click
menu is no longer necessary.

TEST=manual
BUG= 796030 

Change-Id: I6afb4c90cb0011ad588d3182433785099b2e44ef
Reviewed-on: https://chromium-review.googlesource.com/844048
Reviewed-by: Evan Stade <estade@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528851}
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ash/message_center/message_center_view.cc
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ash/message_center/message_center_view.h
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ui/message_center/BUILD.gn
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ui/message_center/views/message_popup_collection.cc
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ui/message_center/views/notification_menu_model.cc
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ui/message_center/views/notification_menu_model_unittest.cc
[modify] https://crrev.com/3090b8bbebb702a4f7c823a8141a4107919bc17c/ui/strings/ui_strings.grd