Pinned tab notification doesn't have the caret and shown across all tabs

[srirambv]

Test plan

#8866 (comment)

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• Did you search for similar issues before submitting this one?
  Yes

• Describe the issue you encountered:
  Pinned tab notification doesn't have the caret and shown across all tabs

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Windows 10 x64

• Brave Version (revision SHA):
  rev 0598ddf

• Steps to reproduce:

  1. Pin a tab
  2. Ensure notifcations are shown for the tab, no caret shown on the notification bar indicating which pinned tab
  3. Switch tab when notification is shown for the pinned tab, retains the notification after switch

• Actual result:
  Pinned tab notification doesn't have the caret and shown across all tabs

• Expected result:
  Should show caret in notification bar for pinned tabs and should be contained only with in that tab

• Will the steps above reproduce in a fresh profile? If not what other info can be added?
  Yes

• Is this an issue in the currently released version?
  No

• Can this issue be consistently reproduced?
  Yes

• Extra QA steps:
  1.
  2.
  3.

• Screenshot if needed:
  

• Any related issues:
  Notification Bar Changes #6939 Move page-level alerts to below the tabs bar, and add an overlap nub #6935
  cc: @jonathansampson

[srirambv]

Works as per testplan(#8866 (comment)) but for Slack notification it still doesn't show the carat symbol