DevTools: Fix "Entries disappear after selecting 'Group by Domain' option in 'Performance' Bottom-U…

third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
index ed97566f508f6aed55978ed74d2f0469b718f972..484b1d1c44ecfa013cc3af8e77dc76543aa3522a 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineTreeView.js
@@ -863,7 +863,7 @@ Timeline.AggregatedTimelineTreeView = class extends Timeline.TimelineTreeView {
    */
   _productByEvent(event) {
     var url = TimelineModel.TimelineProfileTree.eventURL(event);
-    if (!url)
+    if (!url || !this._productByURLCache)
       return '';
     if (this._productByURLCache.has(url))
       return this._productByURLCache.get(url);