Unable to reproduce the issue on chrome reported version# 68.0.3440.106 using Windows-10 with steps mentioned below:
1) Launched chrome reported version and loaded the unpacked extension into chrome://extensions
2) Able to see notification popup at bottom right, clicked on notification popup and clicked on background page
3) On Devtools > Console, seen "onClicked key" event got generated.

@Reporter: Please find the attached screencast for your reference and let us know if we missed anything in reproducing the issue, provide your feedback on it which help in further triaging it. Could you please try to test this issue by creating new profile and let us know if the issue still persists.
Note: Tentatively adding UI>Notifications component to it.

Thanks!

Deleted: 875091.mp4 3.6 MB

	875091.mp4 3.6 MB View Download

Thanks for the video. I very clearly see the issue. For some reason, your version of Chrome 68 is not using the native Windows 10 notifications. I (and users of my extension) have this enabled.

From this article: https://www.theverge.com/2018/8/8/17665398/google-chrome-windows-10-notifications-action-center-support

"If you don’t see the new notification support in Chrome just yet, you can always manually enable it in chrome://flags by turning “native notifications” to the enabled state."

Could you see if that setting is disabled for you and try with it enabled?

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Able to reproduce the issue on chrome reported version# 68.0.3440.106 and on latest chrome# 70.0.3527.0 using Windows-10 with the extension provided in comment# 0. As this issue is seen from M-67( from introduction of "native notifications" flag), hence considering this issue as Non-Regression and marking it as Untriaged.
Note: Issue is not seen on Mac and Linux.

Thanks!

Thank you for the report! Sending a fix now..

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8663895cdd19b9ce09aab12f30d4af189a1944d4

commit 8663895cdd19b9ce09aab12f30d4af189a1944d4
Author: Peter Beverloo <peter@chromium.org>
Date: Mon Aug 20 14:05:48 2018

Don't pass -1 as an action index for Windows native notifications

A negative index is used to indicate the default, unset state of the
action button index in the NotificationLaunchId, but this is not the
right value to pass along to NotificationHandlers.

Bug:  875091 
Change-Id: I0d327eb1f3887904a674a6748cc6e9d60ec783c3
Reviewed-on: https://chromium-review.googlesource.com/1180973
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584430}
[modify] https://crrev.com/8663895cdd19b9ce09aab12f30d4af189a1944d4/chrome/browser/notifications/notification_platform_bridge_win.cc
[modify] https://crrev.com/8663895cdd19b9ce09aab12f30d4af189a1944d4/chrome/browser/notifications/notification_platform_bridge_win_interactive_uitest.cc

+govind fyi - we'll verify the fix in #c7 in Canary tomorrow and will likely request merge. It's a small, safe change that fixes behaviour for a number of extensions that rely on notification click events.

Pls update bug with canary result tomorrow. Also this is regressed in M68, is it critical to merge to M69 this late in release cycle?

The NextAction date has arrived: 2018-08-21

I tested the extension without Peter's fix and on Canary. 

Without Peter's fix, when you click...

1) the notification itself and then...
2) the button in it...

... you get these traces...
onButtonClicked key -1
onButtonClicked key 0

On Canary, you get instead:
onClicked key
onButtonClicked key 0

... so I think this is fixed.

Thank you for confirming, Finnur!

Given the very narrow focus of the CL in #c7 I'd like to request merge of that CL to M69. It will restore functionality in a number of extensions that display notifications.

This bug requires manual review: We are only 13 days from stable.
Please contact the milestone owner if you have questions.
Owners: amineer@(Android), kariahda@(iOS), cindyb@(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Thank you finnur@ and peter@.
Approving merge to M69 branch based on comments #8, #11, #12 and per offline chat with peter@. Please merge now. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e62fc0ef14b8947a1cbbe754feb8a7b137c2f139

commit e62fc0ef14b8947a1cbbe754feb8a7b137c2f139
Author: Peter Beverloo <peter@chromium.org>
Date: Tue Aug 21 16:42:34 2018

Don't pass -1 as an action index for Windows native notifications

A negative index is used to indicate the default, unset state of the
action button index in the NotificationLaunchId, but this is not the
right value to pass along to NotificationHandlers.

Bug:  875091 
Change-Id: I0d327eb1f3887904a674a6748cc6e9d60ec783c3
Reviewed-on: https://chromium-review.googlesource.com/1180973
Commit-Queue: Peter Beverloo <peter@chromium.org>
Reviewed-by: Finnur Thorarinsson <finnur@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#584430}(cherry picked from commit 8663895cdd19b9ce09aab12f30d4af189a1944d4)
Reviewed-on: https://chromium-review.googlesource.com/1183602
Cr-Commit-Position: refs/branch-heads/3497@{#736}
Cr-Branched-From: 271eaf50594eb818c9295dc78d364aea18c82ea8-refs/heads/master@{#576753}
[modify] https://crrev.com/e62fc0ef14b8947a1cbbe754feb8a7b137c2f139/chrome/browser/notifications/notification_platform_bridge_win.cc
[modify] https://crrev.com/e62fc0ef14b8947a1cbbe754feb8a7b137c2f139/chrome/browser/notifications/notification_platform_bridge_win_interactive_uitest.cc

 Issue 882806  has been merged into this issue.