Changes lastN event params to leaving and entering endpoint IDs.

Uses leavingIDs to more efficiently iterate over remote videos.

conference.js

         });
 
         room.on(
-            ConferenceEvents.LAST_N_ENDPOINTS_CHANGED, (ids, enteringIds) => {
-                APP.UI.handleLastNEndpoints(ids, enteringIds);
+            ConferenceEvents.LAST_N_ENDPOINTS_CHANGED,
+            (leavingIds, enteringIds) => {
+                APP.UI.handleLastNEndpoints(leavingIds, enteringIds);
         });
 
         room.on(

modules/UI/UI.js

     VideoLayout.onDominantSpeakerChanged(id);
 };
 
-UI.handleLastNEndpoints = function (ids, enteringIds) {
-    VideoLayout.onLastNEndpointsChanged(ids, enteringIds);
+UI.handleLastNEndpoints = function (leavingIds, enteringIds) {
+    VideoLayout.onLastNEndpointsChanged(leavingIds, enteringIds);
 };
 
 /**

modules/UI/videolayout/VideoLayout.js

     /**
      * On last N change event.
      *
-     * @param lastNEndpoints the list of last N endpoints
+     * @param endpointsLeavingLastN the list currently leaving last N
+     * endpoints
      * @param endpointsEnteringLastN the list currently entering last N
      * endpoints
      */
-    onLastNEndpointsChanged (lastNEndpoints, endpointsEnteringLastN) {
-
-        Object.keys(remoteVideos).forEach(
-            id => {
-                if (lastNEndpoints.length > 0
-                    && lastNEndpoints.indexOf(id) < 0
-                    || endpointsEnteringLastN.length > 0
-                        && endpointsEnteringLastN.indexOf(id) > 0) {
-
-                    let remoteVideo = (id) ? remoteVideos[id] : null;
-                    if (remoteVideo) {
-                        remoteVideo.updateView();
-                        if (remoteVideo.isCurrentlyOnLargeVideo())
-                            this.updateLargeVideo(id);
-                    }
-                }
-            });
+    onLastNEndpointsChanged (endpointsLeavingLastN, endpointsEnteringLastN) {
+        if (endpointsLeavingLastN) {
+            endpointsLeavingLastN.forEach(this._updateRemoteVideo, this);
+        }
+
+        if (endpointsEnteringLastN) {
+            endpointsEnteringLastN.forEach(this._updateRemoteVideo, this);
+        }
+    },
+
+    /**
+     * Updates remote video by id if it exists.
+     * @param {string} id of the remote video
+     * @private
+     */
+    _updateRemoteVideo(id) {
+        const remoteVideo = remoteVideos[id];
+        if (remoteVideo) {
+            remoteVideo.updateView();
+            if (remoteVideo.isCurrentlyOnLargeVideo()) {
+                this.updateLargeVideo(id);
+            }
+        }
     },
 
     /**