The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/886df0ee866e5ec7cb32c2e1d376b8cafeadb6a5

commit 886df0ee866e5ec7cb32c2e1d376b8cafeadb6a5
Author: James Wallace-Lee <jamwalla@chromium.org>
Date: Fri Jul 27 18:24:15 2018

Add extension dialog title to accessible node data

Screen readers should read the title ("Add <extension>?") of extension
install dialogs.

Bug:  849910 
Change-Id: I9d37b3810c046419f4c5a3b4428a57cb0a5f3289
Reviewed-on: https://chromium-review.googlesource.com/1135595
Commit-Queue: James Wallace-Lee <jamwalla@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578713}
[modify] https://crrev.com/886df0ee866e5ec7cb32c2e1d376b8cafeadb6a5/chrome/browser/ui/views/extensions/extension_install_dialog_view.cc
[modify] https://crrev.com/886df0ee866e5ec7cb32c2e1d376b8cafeadb6a5/chrome/browser/ui/views/extensions/extension_install_dialog_view.h

Tried testing the issue on latest chrome #70.0.3508.0 by following below steps.
Steps:
1. Launched JAWS.
2.Added chrome extension : https://chrome.google.com/webstore/detail/sound-on-click/ejchjkneplcffgcopialnjofdhhggjik?hl=en-US
4. Navigated to  activate the ‘add to chrome’ button.But could not observe JAWS  reading the contents of the dialog describing the permissions used by the extension, followed by the first button in focus.

jamwalla@ - Could you please confirm whether it is fixed or still work in progress, it would help us in further verfication.

Thanks.!

Google Chrome	69.0.3497.35 (Official Build) dev (64-bit)
Firmware Version	Google_Lulu.6301.136.57

Does not reproduce on Chrome OS. ChromeVox reads the dialog when it appears and you can linear navigate across it to read contents and dismiss dialog.