NOTIFICATIONS_MUTED type has been added.

Chromium changes:

https://source.chromium.org/chromium/chromium/src/+/c737f6c4bf029f8822f873a08986f17f20aca8ae

commit c737f6c4bf029f8822f873a08986f17f20aca8ae
Author: Richard Knoll <knollr@chromium.org>
Date:   Mon Oct 26 11:45:44 2020 +0000

    Show "Notifications muted" notification

    Instead of silently muting notifications we want to let users know that
    there are new notifications without revealing their content. This will
    show a generic notification instead of the actual one and show a counter
    of how many notifications have been muted.

    Bug: 1131375

PERMISSION_REQUEST notification type was deprecated by

https://source.chromium.org/chromium/chromium/src/+/59b0b60663e44f5e4606bad09b634ce5cee95d60

commit 59b0b60663e44f5e4606bad09b634ce5cee95d60
Author: Andy Paicu <andypaicu@chromium.org>
Date:   Fri Jan 24 15:46:51 2020 +0000

    Cleanup all code related to displaying permission prompts as notifications

    Since we're not using any of the notification permission prompt flavors,
    this CL cleans up all the code that was introduced to experiment with
    them.

    Bug: 1029718

chromium_src/chrome/browser/notifications/notification_handler.h

@@ -20,18 +20,20 @@ class NotificationHandler : public NotificationHandler_ChromiumImpl {
     EXTENSION = 2,
     SEND_TAB_TO_SELF = 3,
     TRANSIENT = 4,
-    PERMISSION_REQUEST = 5,
+    // Deprecated
+    // PERMISSION_REQUEST = 5,
     SHARING = 6,
     ANNOUNCEMENT = 7,
     NEARBY_SHARE = 8,
     BRAVE_ADS = 9,
-    MAX = BRAVE_ADS,
+    NOTIFICATIONS_MUTED = 10,
+    MAX = NOTIFICATIONS_MUTED,
   };
 
   // Make sure we know if the original enum gets changed.
   NotificationHandler() {
     DCHECK(static_cast<int>(NotificationHandler_ChromiumImpl::Type::MAX) + 1 ==
-           static_cast<int>(Type::BRAVE_ADS));
+           static_cast<int>(Type::MAX));
   }
 };