The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/59b1aac273d3e1657f4e284ef54fd490fa7f09ab

commit 59b1aac273d3e1657f4e284ef54fd490fa7f09ab
Author: Katie D <katie@chromium.org>
Date: Fri Feb 16 19:42:12 2018

Play tone when no selection found after user requested read selected text.

Tone was provided by UX team.

Bug:  812703 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I2f6010e381831ff622a2c23734c5363e00fe107d
Reviewed-on: https://chromium-review.googlesource.com/922393
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537384}
[modify] https://crrev.com/59b1aac273d3e1657f4e284ef54fd490fa7f09ab/chrome/browser/resources/chromeos/select_to_speak/BUILD.gn
[add] https://crrev.com/59b1aac273d3e1657f4e284ef54fd490fa7f09ab/chrome/browser/resources/chromeos/select_to_speak/earcons/null_selection.ogg
[modify] https://crrev.com/59b1aac273d3e1657f4e284ef54fd490fa7f09ab/chrome/browser/resources/chromeos/select_to_speak/select_to_speak.js

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

Appropriate earcon played when using search + s with no selection. 

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