It's a regression.

This is handled in the system.display API.

The logic was most recently changed here:

https://codereview.chromium.org/2799963003/diff/100001/chrome/browser/extensions/display_info_provider_chromeos.cc

I'm not sure if that introduced the notification or if there was a change to PreopareNotificationAndSetDisplayMode.

There are two scenarios here:
1- display_info_provider_chromeos uses PrepareNotificationAndSetDisplayMode(), which in turn won't show a notification for internal displays only [1].
   - For external displays, I believe we still want to show the notification which gives the user a way to revert the resolution change in case things go wrong, either via the revert button in the notification or automatically via the timer.

2- Despite of [1], internal displays still show the notification for resolution change. This is done in screen_layout_observer [2], which responds to ui_scale changes.
   - I think we can also avoid doing this here for internal displays as in [1].


[1]: https://cs.chromium.org/chromium/src/ash/display/resolution_notification_controller.cc?q=PrepareNotificationAndSetDisplayMode&sq=package:chromium&l=166
[2]: https://cs.chromium.org/chromium/src/ash/system/screen_layout_observer.cc?q=IDS_ASH_STATUS_TRAY_DISPLAY_RESOLUTION_CHANGED&sq=package:chromium&dr=C&l=280

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0f8b53b27c387900b5a5b0dd19e10acbf25f479d

commit 0f8b53b27c387900b5a5b0dd19e10acbf25f479d
Author: Ahmed Fakhry <afakhry@chromium.org>
Date: Fri Jan 12 21:07:52 2018

Don't notify on UI scale changes coming from settings UI

If:
- The mode change results in changing the UI scale.
- The mode change results in changing the display size
  in unified mode.
And the change is coming from the Settings UI, then don't
show a notification from the ScreenLayoutObserver.

BUG= 757874 
TEST=added tests

Change-Id: I66ef8ac91b12e914187b4edc74aa2f6228e47f6c
Reviewed-on: https://chromium-review.googlesource.com/849752
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529065}
[modify] https://crrev.com/0f8b53b27c387900b5a5b0dd19e10acbf25f479d/ash/display/resolution_notification_controller.cc
[modify] https://crrev.com/0f8b53b27c387900b5a5b0dd19e10acbf25f479d/ash/display/resolution_notification_controller_unittest.cc
[modify] https://crrev.com/0f8b53b27c387900b5a5b0dd19e10acbf25f479d/ash/system/screen_layout_observer.cc
[modify] https://crrev.com/0f8b53b27c387900b5a5b0dd19e10acbf25f479d/ash/system/screen_layout_observer.h
[modify] https://crrev.com/0f8b53b27c387900b5a5b0dd19e10acbf25f479d/ash/system/screen_layout_observer_unittest.cc