Merge "Consolidate duplicated unseen change logic and fix inconsistent code"

diff --cc includes/watcheditem/WatchedItemStoreInterface.php
index 54c02d7,b6d7b68..5ff29d0
--- 1/includes/watcheditem/WatchedItemStoreInterface.php
--- 2/includes/watcheditem/WatchedItemStoreInterface.php
+++ b/includes/watcheditem/WatchedItemStoreInterface.php
@@@ -339,10 -335,9 +339,10 @@@ interface WatchedItemStoreInterface 
         * Usage of this method should be limited to WatchedItem* classes
         *
         * @param string|null $timestamp Value of wl_notificationtimestamp from the DB
 -       * @param User $user
 +       * @param UserIdentity $user
         * @param LinkTarget $target
-        * @return string TS_MW timestamp or null
+        * @return string|null TS_MW timestamp or null if all revision were seen
         */
 -      public function getLatestNotificationTimestamp( $timestamp, User $user, LinkTarget $target );
 +      public function getLatestNotificationTimestamp(
 +              $timestamp, UserIdentity $user, LinkTarget $target );
  }