Rediscover your own notifications.

This new API, NotificationManager.getActiveNotifications(),
allows an app to recover the set of notifications it has
posted that are still active (un-cleared, un-canceled,
visible by the user). Along with the Notification object
you'll get the original tag and id you used to post it,
wrapped up in the somewhat awkwardly-named
StatusBarNotification data structure (previously only used
internally by NoMan/SysUI and NotificationListenerServices).

Bug: 17320461
Change-Id: I8cd610956fafed4e31526b663cebdc31231ad930