We should DEFINITELY not be showing the "dear monitor" message here. I've filed  bug 608027  to track that.

The key question is are there there enough users who want this to justify its creation?

Trying to figure out how to do this in a performant way would be tricky.

Hi Google team,
Sentry unit contain 2 type c ports.
we cannot avoid end-user output their screen to external monitors via 2 type c cables.
while perform a presentation with 2 external monitors, clone mode is more useful then extend mode.
current image cannot support clone mode and display mode switch may cause confusion of end-user

@oshima do we have plans to support mirroring across 2 external displays? If not, we should disable the ability to do that in Settings.

I thought this is already disabled in settings, and shortcut is ignored.

stevenjb@, afakhry@, what's the current status?

'Mirroring' is only shown in the UI when there are 2 displays (i.e. 1 external display).

Was there something else that needs to be disabled in the UI with 3+ displays?

It seems that this bug is a feature request to support mirroring from 3+ displays. Am I correct?

Yes, if we aren't exposing it to users then this issue is only about supporting it for 3+ displays. Updating the title and adding in ovanieva for multi-display.

 Issue 589319  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bafe78889d58613c2aaae534d5154840fb66b995

commit bafe78889d58613c2aaae534d5154840fb66b995
Author: Weidong Guo <weidongg@chromium.org>
Date: Tue Oct 31 17:44:16 2017

multi-display-mirroring: Prerequisite clean up

This CL is a prerequisite CL for supporting mirroring across 3+
displays.
Changes:
1. Clean up old code of mirror mode in display manager and make software
and hardware mirroring more intuitive.
2. Fix a bug that misuses mirroring destination display as source in
display_info_provider_chromeos.cc

Design doc:
go/multi-display-mirroring

BUG= 607844 

Change-Id: I38a065e2693c1094d9b460dd99ad0b2daabd0215
Reviewed-on: https://chromium-review.googlesource.com/734799
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512867}
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/cursor_window_controller.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/display_manager_unittest.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/mirror_window_controller.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/mirror_window_controller.h
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/mirror_window_controller_unittest.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/mirror_window_test_api.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/mirror_window_test_api.h
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/display/root_window_transformers_unittest.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/system/screen_layout_observer.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ash/system/screen_layout_observer_unittest.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/chrome/browser/extensions/display_info_provider_chromeos.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/chrome/browser/extensions/display_info_provider_chromeos_unittest.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ui/display/manager/chromeos/display_configurator.h
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ui/display/manager/display_manager.cc
[modify] https://crrev.com/bafe78889d58613c2aaae534d5154840fb66b995/ui/display/manager/display_manager.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/92aa97948dbf94c5316014b00d7652f2e644e4e8

commit 92aa97948dbf94c5316014b00d7652f2e644e4e8
Author: Weidong Guo <weidongg@chromium.org>
Date: Thu Nov 16 05:08:49 2017

multi-display-mirroring: Implement hardware mirroring

Changes:
1. Support hardware mirroring by adding function to find/create mirror
   mode for 2+ displays.
2. Add unit tests.

Design doc:
go/multi-display-mirroring

BUG= 607844 
TEST=DisplayConfiguratorTest.*

Change-Id: If3371fcfa66b6c5a121a1f1401085df777638b4e
Reviewed-on: https://chromium-review.googlesource.com/731658
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516995}
[modify] https://crrev.com/92aa97948dbf94c5316014b00d7652f2e644e4e8/ui/display/manager/chromeos/display_configurator.cc
[modify] https://crrev.com/92aa97948dbf94c5316014b00d7652f2e644e4e8/ui/display/manager/chromeos/display_configurator.h
[modify] https://crrev.com/92aa97948dbf94c5316014b00d7652f2e644e4e8/ui/display/manager/chromeos/display_configurator_unittest.cc