Issue 869598  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/02e9b8fe2ed32fcdbeef49f5c652adfe4f3f1601

commit 02e9b8fe2ed32fcdbeef49f5c652adfe4f3f1601
Author: Takumi Fujimoto <takumif@chromium.org>
Date: Mon Sep 10 19:23:36 2018

[Harmony Cast Dialog] Give the "no devices found" info button a label

Give the info button a label read by screen readers when it is in focus:
"No Cast destinations found. Need help?"

Bug:  869600 
Change-Id: I90af935d528f7aa128469b98ecb691f6d13228a0
Reviewed-on: https://chromium-review.googlesource.com/1214044
Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590017}
[modify] https://crrev.com/02e9b8fe2ed32fcdbeef49f5c652adfe4f3f1601/chrome/browser/ui/views/media_router/cast_dialog_no_sinks_view.cc

Tested this issue on build without fix 70.0.3507.0 using Mac 10.12.6 and on the latest chrome version 71.0.3549.0.
Steps:
---------
(1) Launched chrome.
(2) Enabled Voice Over by pressing ‘command key+FN key+F5’
(3) Clicked on Cast icon in toolbar
(4) Pressed tab to highlight the No devices found label.
(5) Pressed space bar key.
We have Observed that voice reads "No Cast destinations found. Need help?" but not reads that "link to No Cast Devices Found Help Center Article. Press x button to open link".
@Takumi Fujimoto: Please find the attached screen-cast and let us know if we have missed anything in the process. Could you please help in verifying the fix. 

Thanks!

Deleted: 869600.mp4 2.3 MB

	869600.mp4 2.3 MB View Download

I haven't addressed all the issues that were raised. I'd rather not add "press _ to open link" because I don't explicitly control which key triggers the action, and it may be platform-specific. On Mac and Windows the icon can be activated with space, and I think that's fine.

I think the bigger issue here is that when the help article opens in a new tab, no announcement is made by the screen reader to indicate that a page was opened. So I think it'd be good for us to close the dialog at that point, so that the focus moves to the tab and it gets read.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6edc2ff8d6e6e0aa72584e74530bb4eac452b70b

commit 6edc2ff8d6e6e0aa72584e74530bb4eac452b70b
Author: Takumi Fujimoto <takumif@chromium.org>
Date: Thu Oct 11 22:51:31 2018

[Harmony Cast Dialog] Update the a11y label on "no devices found" button

Make the accessibility label of the "no devices found" button explicitly
state that it opens a help center article in a new tab.

Bug:  869600 
Change-Id: I720eab993d319a53d5faeafb92e5f0bbc1e2d0ee
Reviewed-on: https://chromium-review.googlesource.com/c/1277865
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598992}
[modify] https://crrev.com/6edc2ff8d6e6e0aa72584e74530bb4eac452b70b/chrome/app/media_router_strings.grdp
[modify] https://crrev.com/6edc2ff8d6e6e0aa72584e74530bb4eac452b70b/chrome/browser/ui/views/media_router/cast_dialog_no_sinks_view.cc

I looked into ways to announce the help center tab when it's opened, but didn't have a good solution. So I've updated the screen reader label to mention that it opens a new tab.

It'd be difficult to state which button activates the button, given that's platform dependent (e.g. enter works on Win but not on Mac).

Krishna, is it possible for us to ensure that the string landed in #7 is localized for M71?

yes, it will get picked for M71 translation.

Thanks!