NotificationViewMD currently uses custom ViewTargerter to support clicks on notification.

NotificationViewMD::TargetForRect

Even though it's not clean and maintainable, this is still necessary right now because simply removing this method causes regression on mouse cursor (GetCursor will not be called properly).

https://cs.chromium.org/chromium/src/ui/message_center/views/notification_view_md.cc?l=391&rcl=6bea6c0eb5b6d5f75fb319e577ea124c9fca6723