The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/3e826e5f9c5936934a55c7d45477f32f0e391430

commit 3e826e5f9c5936934a55c7d45477f32f0e391430
Author: Yuichiro Hanada <yhanada@chromium.org>
Date: Thu Oct 11 17:22:44 2018

Hide ARC IME by pressing the back button on the shelf.

Pressing the buck button while the ARC IME shows up should hide the
virtual keyboard.
Note that this CL doesn't change the behavior of the back button
in the browser window because it doesn't generate the key
event.

Bug: 845079,  894362 
Change-Id: I49de330462339cfc89490827f5e65cc1aef60368
Reviewed-on: https://chromium-review.googlesource.com/c/1276085
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598815}
[modify] https://crrev.com/3e826e5f9c5936934a55c7d45477f32f0e391430/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.cc

I left one review comment in the CL above. Nor urgent, but please address it in M72.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/24d31c4684075d9c90d8d1a8ee67400a74501a2e

commit 24d31c4684075d9c90d8d1a8ee67400a74501a2e
Author: Yuichiro Hanada <yhanada@chromium.org>
Date: Thu Oct 11 23:28:12 2018

Show rotated back button while ARC IME shows up.

While ARC IME shows up, the back button is used for hiding the virtual
keyboard. This CL rotates the back button while ARC IME shows up to
align with the behavior.

Bug: 845079,  894362 
Test: Ran on DUT
Change-Id: Ib96249fa7e9cae23b6b6810780b30c00ba4874c8
Reviewed-on: https://chromium-review.googlesource.com/c/1275987
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599007}
[modify] https://crrev.com/24d31c4684075d9c90d8d1a8ee67400a74501a2e/ash/shelf/shelf_view.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/820d766b0b830323ba7dabbfbae4123fd47fd3e8

commit 820d766b0b830323ba7dabbfbae4123fd47fd3e8
Author: Yuichiro Hanada <yhanada@chromium.org>
Date: Fri Oct 12 21:08:14 2018

Consume the back button press only when ARC IME shows.

Bug:  894362 , 845079
Test: The back button works as history back when ARC IME doesn't show up.
Change-Id: Ibffbf39f02f9bc3c75c42b4091dce442046d48e2
Reviewed-on: https://chromium-review.googlesource.com/c/1278511
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599350}
[modify] https://crrev.com/820d766b0b830323ba7dabbfbae4123fd47fd3e8/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.cc
[modify] https://crrev.com/820d766b0b830323ba7dabbfbae4123fd47fd3e8/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.h

I'm requesting merge the CL in comment 5 to M-71. Without this CL, the back button on the shelf doesn't work while ARC++ IME is enabled even if the VK is not visible.

Your change meets the bar and is auto-approved for M71. Please go ahead and merge the CL to branch 3578 manually. Please contact milestone owner if you have questions.
Owners: benmason@(Android), kariahda@(iOS), kbleicher@(ChromeOS), govind@(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/+/b78516ac13f7f93836a960877766421d33d158f4

commit b78516ac13f7f93836a960877766421d33d158f4
Author: Yuichiro Hanada <yhanada@chromium.org>
Date: Wed Oct 17 02:17:30 2018

Consume the back button press only when ARC IME shows.

Bug:  894362 , 845079
Test: The back button works as history back when ARC IME doesn't show up.
Change-Id: Ibffbf39f02f9bc3c75c42b4091dce442046d48e2
Reviewed-on: https://chromium-review.googlesource.com/c/1278511
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#599350}(cherry picked from commit 820d766b0b830323ba7dabbfbae4123fd47fd3e8)
Reviewed-on: https://chromium-review.googlesource.com/c/1285492
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#81}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}
[modify] https://crrev.com/b78516ac13f7f93836a960877766421d33d158f4/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.cc
[modify] https://crrev.com/b78516ac13f7f93836a960877766421d33d158f4/chrome/browser/chromeos/arc/input_method_manager/arc_input_method_manager_service.h

The following revision refers to this bug: 
https://chromium.googlesource.com/chromium/src.git/+/b78516ac13f7f93836a960877766421d33d158f4

Commit: b78516ac13f7f93836a960877766421d33d158f4
Author: yhanada@chromium.org
Commiter: yhanada@chromium.org
Date: 2018-10-17 02:17:30 +0000 UTC

Consume the back button press only when ARC IME shows.

Bug:  894362 , 845079
Test: The back button works as history back when ARC IME doesn't show up.
Change-Id: Ibffbf39f02f9bc3c75c42b4091dce442046d48e2
Reviewed-on: https://chromium-review.googlesource.com/c/1278511
Commit-Queue: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yusuke Sato <yusukes@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#599350}(cherry picked from commit 820d766b0b830323ba7dabbfbae4123fd47fd3e8)
Reviewed-on: https://chromium-review.googlesource.com/c/1285492
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#81}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}