make timeline set threadId public

src/models/event-timeline-set.js

@@ -68,7 +68,7 @@ function EventTimelineSet(room, opts) {
     // just a list - *not* ordered.
     this._timelines = [this._liveTimeline];
     this._eventIdToTimeline = {};
-    this._threadId = opts.threadId;
+    this.threadId = opts.threadId;
     this._filter = opts.filter || null;
 }
 utils.inherits(EventTimelineSet, EventEmitter);

src/models/event-timeline.js

@@ -302,7 +302,7 @@ EventTimeline.prototype.addEvent = function(event, atStart) {
 
     // only call setEventMetadata on the unfiltered timelineSets
     const timelineSet = this.getTimelineSet();
-    if (timelineSet._threadId ||  (timelineSet.room &&
+    if (timelineSet.threadId ||  (timelineSet.room &&
         timelineSet.room.getUnfilteredTimelineSet() === timelineSet)) {
         EventTimeline.setEventMetadata(event, stateContext, atStart);