The flyout loads no more than 25 notifications
from a given source. Using those in-memory notification
objects to count how many are currently unread (and
update the badge) produces a result of at most 25.
This patch extracts the responsibility or counting the
unread from the Model/Item/Groupitem structure into
a new UnreadNotificationCounter class. It receives
estimated updates from other components and synchronizes
with the server after markRead/markUnread operations
have completed.
Bug: T129726
Change-Id: I9af4defc00dd491ed2b355eb4e85073476e08ce7
