The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/138f2bbb67216d68bfc2c1ba95806bbcd11300cb

commit 138f2bbb67216d68bfc2c1ba95806bbcd11300cb
Author: Tetsui Ohkubo <tetsui@chromium.org>
Date: Thu Jul 26 08:10:35 2018

Unified: Disable collapse button when ChromeVox on

New system menu implements collapsed mode which hides some buttons and
sliders that are not really used frequently. It's better for usability
that the button is disabled on ChromeVox.

TEST=manual
BUG= 867798 

Change-Id: Ie238160a6b84f80c8a5c25f4035307d4a668c00c
Reviewed-on: https://chromium-review.googlesource.com/1151071
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578239}
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/collapse_button.cc
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/collapse_button.h
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/top_shortcuts_view.cc
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/top_shortcuts_view.h
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/unified_system_tray_controller.cc
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/unified_system_tray_controller_unittest.cc
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/unified_system_tray_model.cc
[modify] https://crrev.com/138f2bbb67216d68bfc2c1ba95806bbcd11300cb/ash/system/unified/unified_system_tray_model.h

 Issue 871138  has been merged into this issue.