And scroll to offscreen nodes when reading them.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/c36c604e3508c187ff12224a40d06c698f640981

commit c36c604e3508c187ff12224a40d06c698f640981
Author: Katie D <katie@chromium.org>
Date: Fri Feb 16 17:08:49 2018

Read offscreen nodes when speaking selected text with search+s.

The next change will follow onto this one by scrolling to the
currently spoken node if it is offscreen.

Bug:  812874 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I9ad68a2e88885ea7e94f09eb95b8b689eb9a0fd2
Reviewed-on: https://chromium-review.googlesource.com/923085
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537330}
[modify] https://crrev.com/c36c604e3508c187ff12224a40d06c698f640981/chrome/browser/resources/chromeos/select_to_speak/select_to_speak.js

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0475b9d3f8a02b0455ecdc50cff267daa0ec0edd

commit 0475b9d3f8a02b0455ecdc50cff267daa0ec0edd
Author: Katie D <katie@chromium.org>
Date: Wed Feb 21 18:54:30 2018

Scroll to offscreen nodes when reading them from search+s mode.

Stops automatically scrolling as soon as the user initiates a scroll,
under the assumption that they want control of the page scroll.

Bug:  812874 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1ee73c9772bbf1d5a4cf5ba8567d7b0ad413c8e9
Reviewed-on: https://chromium-review.googlesource.com/923162
Commit-Queue: Katie Dektar <katie@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#538168}
[modify] https://crrev.com/0475b9d3f8a02b0455ecdc50cff267daa0ec0edd/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

Steps:

# Go to https://en.wikipedia.org/wiki/Platypus
# select a bunch of text
# Scroll so that part of it is offscreen
# Press ctrl + s to start STS
The page scrolls to put the offscreen text on screen and then reads it.
During the scroll it briefly puts focus on the top of the screen but corrects itself and puts focus on the text as expected. 

Verified. 

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