The logic of UpdateCheckMark() is used by three files,
1. ash/common/system/tray_accessibility.cc
2. ash/common/system/chromeos/audio/audio_detailed_view.cc
3. ash/common/system/chromeos/palette/common_palette_tool.cc

Can I add two files, named as following,
ash/common/system/utils.h
ash/common/system/utils.cc

To add maybe two functions, CheckMark(...) && UncheckMark(...). Each function maybe 3 -5 lines.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c345ab7d5a956251b46048138972883c89337d8e

commit c345ab7d5a956251b46048138972883c89337d8e
Author: minch <minch@chromium.org>
Date: Fri Apr 07 22:23:39 2017

Reuse the code within UpdateCheckMark()

Move UpdateCheckMark() from anonymous namespace of tray_accessibility.cc to tray_popup_utils.h
Then, it can be reused by AudioDetailedView and CommonPaletteTool.

BUG= 707851 

Review-Url: https://codereview.chromium.org/2803893002
Cr-Commit-Position: refs/heads/master@{#463020}

[modify] https://crrev.com/c345ab7d5a956251b46048138972883c89337d8e/ash/common/system/chromeos/audio/audio_detailed_view.cc
[modify] https://crrev.com/c345ab7d5a956251b46048138972883c89337d8e/ash/common/system/chromeos/palette/common_palette_tool.cc
[modify] https://crrev.com/c345ab7d5a956251b46048138972883c89337d8e/ash/common/system/tray/tray_popup_utils.cc
[modify] https://crrev.com/c345ab7d5a956251b46048138972883c89337d8e/ash/common/system/tray/tray_popup_utils.h
[modify] https://crrev.com/c345ab7d5a956251b46048138972883c89337d8e/ash/common/system/tray_accessibility.cc