The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4bb33820986292a9fd983b2ca758dcee1cd196f7

commit 4bb33820986292a9fd983b2ca758dcee1cd196f7
Author: Katie D <katie@chromium.org>
Date: Fri Feb 09 19:30:18 2018

Immediately update focus & highlight rather than waiting for hittest.

Because we only set word highlighting after doing an automation
hittest, highlight results with faster speech rates could seem
inconsistent due to the hittest waiting to return.

Also fixes a nit with highlight, and a bug where STS could get stuck
thinking that the selection key was down. Does the latter by making
sure that any keyUp from the selection key updates selection key
state, whether or not selection should be read.

Bug:  810075 , 809732 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I45e62fc15d558ee548e60b4b4aea27ca7d65158d
Reviewed-on: https://chromium-review.googlesource.com/907337
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#535783}
[modify] https://crrev.com/4bb33820986292a9fd983b2ca758dcee1cd196f7/chrome/browser/resources/chromeos/select_to_speak/select_to_speak.js
[modify] https://crrev.com/4bb33820986292a9fd983b2ca758dcee1cd196f7/chrome/browser/resources/chromeos/select_to_speak/select_to_speak_mouse_selection_test.extjs
[modify] https://crrev.com/4bb33820986292a9fd983b2ca758dcee1cd196f7/chrome/browser/resources/chromeos/select_to_speak/select_to_speak_unittest.gtestjs

Google Chrome 67.0.3369.0 (Official Build) canary (64-bit)
Firmware Version Google_Samus.6300.276.0
Flag enabled: #enable-experimental-accessibility-features

# Enable STS in Accessibility Settings
# In STS settings, make speech rate Fastest.
# Launch article with a lot of text such as https://en.wikipedia.org/wiki/Platypus
# Highlight a large quantity of text using the mouse
# Press search + s to start reading
Highlight ring and word highlighting are rendered as expected with no problems keeping up with speech

# Hold down search and drag highlight over large amount of text
Highlight ring and word highlighting are rendered as expected with no problems keeping up with speech

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