Is this key combo only for whitelisted app? Or for all apps? i.e. Can user toggle between TalkBack and ChromeVox arc native support for non-whitelisted app?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/76484cb1ccf68c5724c6f185b2ef55965d60a0e2

commit 76484cb1ccf68c5724c6f185b2ef55965d60a0e2
Author: David Tseng <dtseng@chromium.org>
Date: Mon Oct 02 21:20:39 2017

Add a command to turn on ChromeVox or TalkBack support in an ARC++ app

Bug:  709109 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I5a7f10b3cc0d62ad7baab56e380e77a860ca2a5a
Reviewed-on: https://chromium-review.googlesource.com/677095
Reviewed-by: Oliver Chang <ochang@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Yuki Awano <yawano@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#505786}
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/accessibility/accessibility_extension_api.cc
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/accessibility/accessibility_extension_api.h
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge.cc
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/chromeos/arc/accessibility/arc_accessibility_helper_bridge.h
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/chromeos/arc/accessibility/ax_tree_source_arc.cc
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/resources/chromeos/chromevox/chromevox/background/keymaps/next_keymap.json
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/browser/resources/chromeos/chromevox/cvox2/background/command_handler.js
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/chrome/common/extensions/api/accessibility_private.json
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/components/arc/common/accessibility_helper.mojom
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/extensions/browser/extension_function_histogram_value.h
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/third_party/closure_compiler/externs/accessibility_private.js
[modify] https://crrev.com/76484cb1ccf68c5724c6f185b2ef55965d60a0e2/tools/metrics/histograms/enums.xml