incorporate PR feedback

lib/models/room.js

@@ -696,15 +696,12 @@ Room.prototype._addLiveEvent = function(event, duplicateStrategy) {
             event.sender.userId, event, "m.read"
         ), true);
 
-        // also, any live events from a user should be taken as implicit
+        // Any live events from a user could be taken as implicit
         // presence information: evidence that they are currently active.
         // ...except in a world where we use 'user.currentlyActive' to reduce
         // presence spam, this isn't very useful - we'll get a transition when
-        // they are no longer currently active anyway. so comment it out for now.
-
-        // var user = this.currentState.getMember(events[i].sender.userId);
-        // user.lastActiveAgo = 0;
-        // user.lastPresenceTs = Date.now();
+        // they are no longer currently active anyway. So don't bother to
+        // reset the lastActiveAgo and lastPresenceTs from the RoomState's user.
     }
 };
 

lib/models/user.js

@@ -143,6 +143,15 @@ User.prototype.getLastModifiedTime = function() {
     return this._modified;
 };
 
+/**
+ * Get the absolute timestamp when this User was last known active on the server.
+ * It is *NOT* accurate if this.currentlyActive is true.
+ * @return {number} The timestamp
+ */
+User.prototype.getLastActiveTs = function() {
+    return this.lastPresenceTs - this.lastActiveAgo;
+};
+
 /**
  * The User class.
  */