The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7dfd14861ec196544b5a71171c08638a45c7f0a4

commit 7dfd14861ec196544b5a71171c08638a45c7f0a4
Author: Weidong Guo <weidongg@chromium.org>
Date: Wed Nov 08 05:56:28 2017

multi-display-mirroring: Implement software mirroring

Changes:
1. Add a flag enable-multi-mirroring for all following and
future changes for supporting multiple display mirroring.
2. Do software mirroring across 3+ displays.
3. Enable cursor compositing for software mirroring.
4. Add unit tests.

Design doc:
go/multi-display-mirroring

BUG= 782291 , 782292 
TEST=MultiMirroringTest.*

Change-Id: Ia684379a19c1630a45c82e4f328e4d8ab3a238f4
Reviewed-on: https://chromium-review.googlesource.com/747055
Commit-Queue: Weidong Guo <weidongg@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514768}
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/cursor_window_controller.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/cursor_window_controller.h
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/cursor_window_controller_unittest.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/display_configuration_controller.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/display_manager_unittest.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/mirror_window_controller_unittest.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/root_window_transformers_unittest.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/display/window_tree_host_manager.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/shell.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/system/screen_layout_observer.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ash/system/screen_layout_observer_unittest.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/chrome/browser/about_flags.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/testing/buildbot/filters/ash_unittests_mash.filter
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ui/display/display_switches.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ui/display/display_switches.h
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ui/display/manager/display_manager.cc
[modify] https://crrev.com/7dfd14861ec196544b5a71171c08638a45c7f0a4/ui/display/manager/display_manager.h