You cannot trigger the menu between apps.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/eb4b0458484d5e9c032c68f02ea0f95ad8518272

commit eb4b0458484d5e9c032c68f02ea0f95ad8518272
Author: Alex Newcomer <newcomer@chromium.org>
Date: Tue Aug 21 16:51:52 2018

cros: Show context menu between gaps in apps in homecher mode.

Show a context menu between apps in homecher-tablet mode.
Don't show a menu between apps in laptop mode.

Bug:  869623 
Change-Id: Idfb8f5d970f7716397ec42769b0e6a8f4473acb1
Reviewed-on: https://chromium-review.googlesource.com/1180249
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584786}
[modify] https://crrev.com/eb4b0458484d5e9c032c68f02ea0f95ad8518272/ash/app_list/test/app_list_test_view_delegate.cc
[modify] https://crrev.com/eb4b0458484d5e9c032c68f02ea0f95ad8518272/ash/app_list/test/app_list_test_view_delegate.h
[modify] https://crrev.com/eb4b0458484d5e9c032c68f02ea0f95ad8518272/ash/app_list/views/app_list_view.cc
[modify] https://crrev.com/eb4b0458484d5e9c032c68f02ea0f95ad8518272/ash/app_list/views/app_list_view_unittest.cc

:D