Yes I think since now tablet mode is controlled by whether there is mouse or touchpad, we cannot show/hide virtual keyboard based on tablet mode state.

I think we can do what the overview tray does currently which is shown when the built in keyboard has its events blocked instead of based on tablet mode. Then in the future we can update both to take care of case of external keyboards as well.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4

commit a675cecf91f666b2d78a7c1c26b6a8ae330b95b4
Author: Sammie Quon <sammiequon@google.com>
Date: Thu Sep 06 17:50:38 2018

cros: Show the VK when in clamshell mode with no keyboard.

Its possible for users to enter clamshell but still need the VK by
plugging in an external mouse. This cl check whether the internal
keyboard is disabled to determine showing or hiding VK instead of just
tablet mode or not.

TabletModeController is getting a lot of friend test class, so also
introduce TabletModeControllerTestApi.

Test: ash_unittests
Bug:  878795 
Change-Id: I0b6e07ef6833e00dd1b6d5358ad7aca4e63a12e5
Reviewed-on: https://chromium-review.googlesource.com/1198486
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589209}
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/BUILD.gn
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/keyboard/virtual_keyboard_controller.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/keyboard/virtual_keyboard_controller.h
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/keyboard/virtual_keyboard_controller_unittest.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/system/overview/overview_button_tray.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/system/overview/overview_button_tray_unittest.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_controller.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_controller.h
[add] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_controller_test_api.cc
[add] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_controller_test_api.h
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_controller_unittest.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/ash/wm/tablet_mode/tablet_mode_window_manager_unittest.cc
[modify] https://crrev.com/a675cecf91f666b2d78a7c1c26b6a8ae330b95b4/chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos_unittest.cc

Issue 870924 has been merged into this issue.

+geohsu for merge permissions

This bug requires manual review: We are only 6 days from stable.
Please contact the milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), geohsu@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379

commit b21bb5824fd9e10b5849a43c9b96bb2e00b6e379
Author: Sammie Quon <sammiequon@google.com>
Date: Wed Oct 10 05:22:15 2018

[merge to 70] cros: Show the VK when in clamshell mode with no keyboard.

Its possible for users to enter clamshell but still need the VK by
plugging in an external mouse. This cl check whether the internal
keyboard is disabled to determine showing or hiding VK instead of just
tablet mode or not.

TabletModeController is getting a lot of friend test class, so also
introduce TabletModeControllerTestApi.

TBR=sammiequon@google.com

(cherry picked from commit a675cecf91f666b2d78a7c1c26b6a8ae330b95b4)

Test: ash_unittests
Bug:  878795 
Change-Id: I0b6e07ef6833e00dd1b6d5358ad7aca4e63a12e5
Reviewed-on: https://chromium-review.googlesource.com/1198486
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#589209}
Reviewed-on: https://chromium-review.googlesource.com/c/1272028
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#942}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/BUILD.gn
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/keyboard/virtual_keyboard_controller.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/keyboard/virtual_keyboard_controller.h
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/keyboard/virtual_keyboard_controller_unittest.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/system/overview/overview_button_tray.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/system/overview/overview_button_tray_unittest.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_controller.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_controller.h
[add] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_controller_test_api.cc
[add] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_controller_test_api.h
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_controller_unittest.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/ash/wm/tablet_mode/tablet_mode_window_manager_unittest.cc
[modify] https://crrev.com/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379/chrome/browser/ui/ash/multi_user/multi_user_window_manager_chromeos_unittest.cc

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/b21bb5824fd9e10b5849a43c9b96bb2e00b6e379

Commit: b21bb5824fd9e10b5849a43c9b96bb2e00b6e379
Author: sammiequon@google.com
Commiter: sammiequon@chromium.org
Date: 2018-10-10 05:22:15 +0000 UTC

[merge to 70] cros: Show the VK when in clamshell mode with no keyboard.

Its possible for users to enter clamshell but still need the VK by
plugging in an external mouse. This cl check whether the internal
keyboard is disabled to determine showing or hiding VK instead of just
tablet mode or not.

TabletModeController is getting a lot of friend test class, so also
introduce TabletModeControllerTestApi.

TBR=sammiequon@google.com

(cherry picked from commit a675cecf91f666b2d78a7c1c26b6a8ae330b95b4)

Test: ash_unittests
Bug:  878795 
Change-Id: I0b6e07ef6833e00dd1b6d5358ad7aca4e63a12e5
Reviewed-on: https://chromium-review.googlesource.com/1198486
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#589209}
Reviewed-on: https://chromium-review.googlesource.com/c/1272028
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/branch-heads/3538@{#942}
Cr-Branched-From: 79f7c91a2b2a2932cd447fa6f865cb6662fa8fa6-refs/heads/master@{#587811}