The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/390ff9702c40b2a62851df467281ac31db3e5073

commit 390ff9702c40b2a62851df467281ac31db3e5073
Author: Katie Dektar <katydek@google.com>
Date: Tue Jan 09 03:03:02 2018

Fix select-to-speak focus ring drawing in ARC++.

Previously the focus ring would quickly be removed because hit testing
returned the wrong window. Now, look for the current focused node
and use that if windows don't match.

The same ARC++ hittest workaround is already in line 444 in Select-to-Speak.

Bug:  793968 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ic9371e9716613a8f06db10fc280e77b0997e7660
Reviewed-on: https://chromium-review.googlesource.com/854944
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#527883}
[modify] https://crrev.com/390ff9702c40b2a62851df467281ac31db3e5073/chrome/browser/resources/chromeos/select_to_speak/select_to_speak.js

Moving from just having STS label to also having the UI>Accessibility>SelectToSpeak component to make searching easier in the future. 

Google Chrome	68.0.3440.15 (Official Build) dev (64-bit)
Firmware Version Google_Lulu.6301.136.57

Tested in non-corp account using Google Play Music app
Steps:
Use STS to highlight several times, checking for flickering or turning off and on

Behaved as expected with continuous highlight