Clicking on Slack notification opens a new tab instead of focusing on existing tab

[srirambv]

Description

Clicking on slack notification opens a new tab instead of focusing on existing tab

Steps to Reproduce

1. Clean profile on 0.54.0
2. Login to slack, enable notifications and pin the tab
3. Set focus to a normal tab and background b-c. Make any other windows app as active app
4. Wait for slack notification to show up
5. Click the windows notification, doesn't bring b-c to focus as active app
6. Switch to b-c, opens a new tab and loads the message that was show in notification and clicked
7. Clicking multiple notifications, opens each new tab for the clicked notifications. Some tabs goes into infinite load and doesn't show message (tab hangs)

Actual result:

Clicking on slack notification opens a new tab instead of focusing on existing tab

Expected result:

Should bring b-c to foreground and only switch to the pinned tab/slack tab instead of opening a new tab each time a notification is clicked

Reproduces how often:

80% (sometimes it does nothing, doesn't focus or highlights b-c

Brave version (about:brave info)

Brave	0.54.0 Chromium: 69.0.3497.32 (Official Build) dev (64-bit)
Revision	bf910299d07564d66b36991ebc7dbdc7e26fe897-refs/branch-heads/3497@{#514}
OS	Windows
JavaScript	V8 6.9.427.14
Flash	(Disabled)

Reproducible on current release:

Website problems only:

• Does the issue resolve itself when disabling Brave Shields?
• Is the issue reproducible on the latest version of Chrome?

Additional Information

Verified the issue on Chrome Beta (69.0.3497.42 (Official Build) beta (64-bit) (cohort: Beta)), switches to pinned slack tab when app is in background and highlights on task bar with flashing taskbar icon. Doesn't open a new tab.

@kjozwiak verified the issue on his Windows machine.
@kjozwiak and @LaurenWags didn't reproduce this on macOS
@bbondy please move the issue to backlog if required.
cc: @emerick