Issue 770243  has been merged into this issue.

Kyle and/or Fady, any pointers as to what needs to be done here? Does this just need some additional mojom calls so that we copy a portion of one display to another?

It's not clear how to make this work in the easiest way. We had discussed this at some point. It was suppose to work something like this afaik:

Display flow:

1. n+1 CompositorFrameSink instances in viz where one is the unified display whose bounds are a union of the attached display::Display objects and the the remaining are 1-1 with the display::Display objects.
2. there is a single FrameGenerator instance corresponding to the unified-display's CFS. From the viewpoint of ScreenManager and all upstream software, only the bounds and existence of the single unified display::Display matters.
3. this "unified mode" FrameGenerator builds CFs for each CompositorFrameSink corresponding to a physical display. These CFs take the surface backing the unified-mode CompositorFrameSink as their source. 
4. It ought to be the case that Surfacesync will do the "right thing" and permit the physical CFS to sync with the completion of the "embedded" unified surface. Hand-waving here...

Input flow: it should just work for mouse events with the presumption that there is a single virtual unified display::Display

mouse pointer: I think we could simply adjust CursorLocationManager and it could do the right thing with help from the UnifiedDesktopLayoutMatrix

high-dpi: is it supported in unified mode? hardware limitations would probably make it impossible (very few GPUs on ChromeOS will support a 8k wide FBO.)

Setup flow:
from the viewpoint of the browser and ash, once we've entered unified mode, the screen contains a single display::Display corresponding to the unified display. So we need to modify ws::ScreenManager so that it can maintain two different views: one is the single unified display for ash, the window tree, etc. and one is for the unified-mode FrameGenerator.

The Ash UI code needs to ask ws::ScreenManager to emit display messages to Ash that disconnect the physical displays and replace them with the unified display. And then configure FrameGenerator to do what I described above.

sky: 
You can test out the current unified mode code in cash with Ozone X11. You'd need a command line something like below. You might need to go enable it in display settings afterwards?

./chrome --ash-host-window-bounds=0+20-900x900,920+20-900x900 --ash-dev-shortcuts --ash-debug-shortcuts --use-first-display-as-internal --ash-enable-unified-desktop

For running mus with Ozone X11 it would be something like the following (which crashes on startup currently):

./chrome --mus --screen-config=900x900/i,900x900 --ash-dev-shortcuts --ash-debug-shortcuts --ash-enable-unified-desktop

I tried --screen-config=800x800,800x800 --mus --ash-debug-shortcuts --ash-dev-shortcuts

And then control-shift-j to toggle unified. This triggers openning another window and the displays don't update, but at least it's not a crash:)

Please consider (or wait for) the changes we're about to land in CL: https://chromium-review.googlesource.com/c/chromium/src/+/683094 to make it possible layout displays in a matrix grid in Unified Mode.

Those changes (hopefully) shouldn't impact most of the work needed here.

Mike said he would take this on, so I'm passing his way.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c

commit 3ded4a2234ea0fde3d5ad44773e1fa56c18f497c
Author: Mike Wasserman <msw@chromium.org>
Date: Fri Oct 20 20:48:33 2017

mus: Plumb DisplayManager software_mirroring_display_list to Mus.

Pass display::DisplayManager's mirror destination displays to Mus.
This will be used to setup mirrored/unified mode for Mus/Mash.

Bug:  764472 
Change-Id: Ib810b52a1c3687c69bae5f810140f4b858fa9f1b
Reviewed-on: https://chromium-review.googlesource.com/726951
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510554}
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ash/mus/bridge/shell_port_mash.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ash/mus/display_synchronizer.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/public/interfaces/window_manager.mojom
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/display_manager.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/display_manager.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/test_utils.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/window_tree.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/window_tree.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/services/ui/ws/window_tree_unittest.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/mus/window_manager_delegate.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/mus/window_tree_client.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/mus/window_tree_client.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/mus/window_tree_host_mus_init_params.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/test/mus/test_window_manager_client.cc
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/aura/test/mus/test_window_manager_client.h
[modify] https://crrev.com/3ded4a2234ea0fde3d5ad44773e1fa56c18f497c/ui/display/manager/display_manager.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/667941c903599fb63a2cd90fe2ccf2700a6c19b7

commit 667941c903599fb63a2cd90fe2ccf2700a6c19b7
Author: Mike Wasserman <msw@chromium.org>
Date: Tue Nov 07 21:00:32 2017

mus: Pass viewport metrics of mirror displays to Mus

These will be used by Mus soon.

Bug:  764472 
Test: None
Change-Id: I3073f6ab7895c5874124b671dd6febb7276c831c
Reviewed-on: https://chromium-review.googlesource.com/756922
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514576}
[modify] https://crrev.com/667941c903599fb63a2cd90fe2ccf2700a6c19b7/ash/mus/display_synchronizer.cc
[modify] https://crrev.com/667941c903599fb63a2cd90fe2ccf2700a6c19b7/services/ui/ws/display_manager.cc
[modify] https://crrev.com/667941c903599fb63a2cd90fe2ccf2700a6c19b7/ui/aura/mus/window_tree_client.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7667c88d3ab1ece545797661deaabcf93aea4d1e

commit 7667c88d3ab1ece545797661deaabcf93aea4d1e
Author: Mike Wasserman <msw@chromium.org>
Date: Tue Nov 07 21:02:50 2017

Move kUnifiedDisplayId to display constants file

DCHECK it's not passed to Mus as the internal display id.

Bug:  764472 
Test: None
Change-Id: I67867faffdb2a2dd501351d38a85bf57a4431bf8
Reviewed-on: https://chromium-review.googlesource.com/757416
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514581}
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/ash/display/cursor_window_controller.cc
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/ash/display/window_tree_host_manager.cc
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/services/ui/ws/display_manager.cc
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/ui/display/manager/display_manager.cc
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/ui/display/manager/display_manager.h
[modify] https://crrev.com/7667c88d3ab1ece545797661deaabcf93aea4d1e/ui/display/types/display_constants.h

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7e534751e74dcf650b6fcb1b394a9ca54b4bee4a

commit 7e534751e74dcf650b6fcb1b394a9ca54b4bee4a
Author: Mike Wasserman <msw@chromium.org>
Date: Fri Nov 10 19:02:44 2017

Mus: Destroy displays with config changes, not root removal.

Destroy Mus ws::Displays when Ash configurations omit them.
Do not destroy displays when the root is removed/destroyed.

WindowManagerDisplayRoot objects are orphaned on display destruction.
They are still only destroyed via ws::WindowTree::DeleteWindow.

Avoids complexity for mus mirroring: http://crrev.com/c/734120

Bug:  764472 
Test: No --mus multi-display or shutdown changes. (Ctrl+Shift+D w/--ash-dev-shortcuts)
Change-Id: Iab096bdb3912ebc515c4c67f0fc04b0f32a79e8a
Reviewed-on: https://chromium-review.googlesource.com/761764
Commit-Queue: Michael Wasserman <msw@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515622}
[modify] https://crrev.com/7e534751e74dcf650b6fcb1b394a9ca54b4bee4a/services/ui/ws/display.cc
[modify] https://crrev.com/7e534751e74dcf650b6fcb1b394a9ca54b4bee4a/services/ui/ws/display_manager.cc
[modify] https://crrev.com/7e534751e74dcf650b6fcb1b394a9ca54b4bee4a/services/ui/ws/window_tree_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/efaa577e8a3ae28af5dbc946d685f0fdef96132a

commit efaa577e8a3ae28af5dbc946d685f0fdef96132a
Author: Mike Wasserman <msw@chromium.org>
Date: Wed Nov 15 18:28:50 2017

mus: Configure displays for mirroring/unified modes

Apply mirroring configurations on linux-desktop chromeos with Mus.
TODO: Add actual mirroring support (destination displays are empty for now)

Check mirrors sent to Mus' SetDisplayConfiguration, create displays as needed.
Do not use Ash's MirrorWindowController and ash-side mirror root windows in Mus.

Allow WindowTree::[Process]SetDisplayRoot to be called with existing displays.
(recreate the ws::Dispay's WindowManagerDisplayRoot as needed in that case)

Revert hardware->software mirroring for Mus on linux-desktop chromeos.
Make DisplayConfiguratorTest simulate on-device use with a commandline flag.

Bug:  764472 
Change-Id: I4fdbb109e77a13819fb396820c9be7a400f4c05f
Reviewed-on: https://chromium-review.googlesource.com/734120
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: kylechar <kylechar@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516752}
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ash/display/mirror_window_controller_unittest.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ash/display/window_tree_host_manager.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/chromeos/system/devicemode.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/services/ui/ws/display.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/services/ui/ws/display.h
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/services/ui/ws/display_manager.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/services/ui/ws/window_tree.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/testing/buildbot/filters/ash_unittests_mash.filter
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/testing/buildbot/filters/ash_unittests_mus.filter
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ui/display/BUILD.gn
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ui/display/manager/chromeos/DEPS
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ui/display/manager/chromeos/display_configurator.cc
[modify] https://crrev.com/efaa577e8a3ae28af5dbc946d685f0fdef96132a/ui/display/manager/chromeos/display_configurator_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a

commit 5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a
Author: Mike Wasserman <msw@chromium.org>
Date: Thu Dec 14 21:34:12 2017

mus: Support the unified display config for mus without viz

Add AshWindowTreeHostMusUnified and AshWindowTreeHostMusMirroringUnified.
(near copies of AshWindowTreeHostUnified and AshWindowTreeHostMirroringUnified)
Make ShellPortMus::CreateAshWindowTreeHost construct these like AshWindowTreeHost::Create.

Loosen DisplayManager::SetDisplayConfiguration restrictions for unified (w/o viz).
Do not show the PlatformDisplay's window for the virtual/offscreen unified display.

TODO: Fix targeting of events on the second display during capture.
TODO: Fix a crash on shutdown when unified mode is still active.

Bug:  764472 , 770243 
TBR: dpranke@chromium.org
Test: Unified mode works reasonably in Mus (needs event handling work)
Change-Id: I25a4f2f917275b4fd9f73cb62a5f22aaf01806ca
Reviewed-on: https://chromium-review.googlesource.com/817761
Commit-Queue: Michael Wasserman <msw@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524186}
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/BUILD.gn
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/DEPS
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/display/mirror_window_controller.cc
[add] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/host/ash_window_tree_host_mus_mirroring_unified.cc
[add] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/host/ash_window_tree_host_mus_mirroring_unified.h
[add] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/host/ash_window_tree_host_mus_unified.cc
[add] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/host/ash_window_tree_host_mus_unified.h
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/ash/shell_port_mus.cc
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/services/ui/ws/display_manager.cc
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/services/ui/ws/platform_display_default.cc
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/testing/buildbot/chromium.chromiumos.json
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/testing/buildbot/chromium.fyi.json
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/testing/buildbot/chromium.memory.json
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/testing/buildbot/filters/BUILD.gn
[delete] https://crrev.com/b992fb57cbd2064f7895a2af938a39e35c17a1a2/testing/buildbot/filters/ash_unittests_mus.filter
[modify] https://crrev.com/5cf0fa8b5e659d6ea48d2e0839dde4e2144a9d9a/testing/buildbot/test_suites.pyl

I have a fix out for review that seems to fix event dispatch during capture:
  https://chromium-review.googlesource.com/c/chromium/src/+/842467

AFAIK, the remaining issues for unified mode in mushrome are:
- Need to test high-dpi and check for issues on-device.
- Mouse warp doesn't seem to work on desktop.
- An extra cursor is shown on the first display on desktop.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/42cd5d0e6fe78cb70fba60c14d27f74d330c1771

commit 42cd5d0e6fe78cb70fba60c14d27f74d330c1771
Author: Mike Wasserman <msw@chromium.org>
Date: Tue Jan 09 19:07:42 2018

mus: Fix unified display event locations during capture.

Pass the root window of the display supplying events from Mus WS to Ash WM.
(Aura can't access Ash's unified mirroring displays via display::Screen)
Dispatch Mus unified located events to the physical display's root window.
(dispatch like classic Ash during capture, use MusUnifiedEventTargeter)

Ignore Mus unified event locations; use their root locations instead.
(Mus attempts to determine local coordinates with incorrect assumptions)
(Mus doesn't know physical display root offsets from the unified root)

Remove unused WindowTreeClientPrivate::CallOnWindowInputEvent().

Bug:  764472 
Test: "chrome --mus --screen-config=400x400,400x400 --ash-dev-shortcuts" + CTRL-SHIFT-J + drag window on 2nd display.
Change-Id: Iaf7da574a487c9bd78ae4238c1687615ccb89c43
Reviewed-on: https://chromium-review.googlesource.com/842467
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528061}
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ash/host/ash_window_tree_host_mus_unified.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/content/renderer/mus/renderer_window_tree_client.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/content/renderer/mus/renderer_window_tree_client.h
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/services/ui/public/interfaces/window_tree.mojom
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/services/ui/ws/test_utils.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/services/ui/ws/test_utils.h
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/services/ui/ws/window_tree.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/services/ui/ws/window_tree_client_unittest.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ui/aura/mus/window_tree_client.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ui/aura/mus/window_tree_client.h
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ui/aura/mus/window_tree_client_unittest.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ui/aura/test/mus/window_tree_client_private.cc
[modify] https://crrev.com/42cd5d0e6fe78cb70fba60c14d27f74d330c1771/ui/aura/test/mus/window_tree_client_private.h

I should have noted this bug in my recent change that uses an offscreen surface for the unified display:

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5697939468e0812830e0362a3e6c1b44c352cfc6

commit 5697939468e0812830e0362a3e6c1b44c352cfc6
Author: Mike Wasserman <msw@chromium.org>
Date: Wed Jan 17 22:38:58 2018

mus: Fix gpu context lost errors and crashes on display removal

Destroy AshWindowTreeHostMus's compositor on shutdown.
(Mus async destroys the underlying platform window)

Destroy displays on root removal, not config changes.
(revert http://crrev.com/c/761764 to match cash dtor ordering)

Use a stub window for Ash's virtual unified display.
(matches cash to use an offscreen surface for rendering)

Bug:   798538  
Test: No errors/crashes removing displays with --mus, mirroring/unified works.
Change-Id: I064416cfc377bf19ec9afa214baa28a75846acf8
Reviewed-on: https://chromium-review.googlesource.com/862603
Commit-Queue: Michael Wasserman <msw@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529930}
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/ash/display/mirror_window_controller.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/ash/host/ash_window_tree_host_mus.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/ash/system/night_light/night_light_controller.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/ash/system/night_light/night_light_controller_unittest.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/services/ui/ws/display.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/services/ui/ws/display_manager.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/services/ui/ws/platform_display_default.cc
[modify] https://crrev.com/5697939468e0812830e0362a3e6c1b44c352cfc6/services/ui/ws/window_tree_unittest.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8443bcccab0cc8a1e88cda27da0ca41d6064cdcb

commit 8443bcccab0cc8a1e88cda27da0ca41d6064cdcb
Author: Mike Wasserman <msw@chromium.org>
Date: Thu Jan 18 19:29:07 2018

mus: Fix missing internal display crash for unified mode

Bug:  801257 ,  764472 
Change-Id: I74ec33e1e1ee35312a43b3bed4e2c1a3042c57b9
Reviewed-on: https://chromium-review.googlesource.com/872460
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#530228}
[modify] https://crrev.com/8443bcccab0cc8a1e88cda27da0ca41d6064cdcb/services/ui/ws/display_manager.cc

I'm going to mark this Fixed, unified display management is generally working in --mus.
There are mouse/touch defects tracked in  Issue 804460 .
There is more work to be done for mus+viz later.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/51935a939ac01a2b974b13836bc9d4061ab33e42

commit 51935a939ac01a2b974b13836bc9d4061ab33e42
Author: Mike Wasserman <msw@chromium.org>
Date: Wed Feb 28 05:10:05 2018

mus+viz: Update mirroring and unified mode todos

TBR=sky@chromium.org

Bug:  764472 ,  806318 
Change-Id: Ife275bdd5eb1aed5f0a8d2117d7796e1a3e1e4cd
Reviewed-on: https://chromium-review.googlesource.com/940780
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#539717}
[modify] https://crrev.com/51935a939ac01a2b974b13836bc9d4061ab33e42/services/ui/ws/display_manager.cc
[modify] https://crrev.com/51935a939ac01a2b974b13836bc9d4061ab33e42/services/ui/ws/window_tree.cc