The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/88bf4fcaa3fc697131ed951b535b23e3793f1cd1

commit 88bf4fcaa3fc697131ed951b535b23e3793f1cd1
Author: Alex Newcomer <newcomer@chromium.org>
Date: Fri Aug 17 22:22:23 2018

cros: Disable context menus on the back and overflow buttons.

UX requests we disable context menus on the back button and overflow
buttons in the shelf.

Removed tests for these cases and added new ones for not showing
the menus.

Bug:  875334 
Change-Id: I45c320a148e8f7ad39abd0e8181e59e3c4b663fe
Reviewed-on: https://chromium-review.googlesource.com/1180073
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584219}
[modify] https://crrev.com/88bf4fcaa3fc697131ed951b535b23e3793f1cd1/ash/shelf/shelf_view.cc
[modify] https://crrev.com/88bf4fcaa3fc697131ed951b535b23e3793f1cd1/ash/shelf/shelf_view_unittest.cc