DevTools: [timeline tree] extract URL from event initiator

Source/devtools/front_end/timeline/TimelineTreeView.js

Index: Source/devtools/front_end/timeline/TimelineTreeView.js
diff --git a/Source/devtools/front_end/timeline/TimelineTreeView.js b/Source/devtools/front_end/timeline/TimelineTreeView.js
index 0bf6de842e1dd08fe1c0206a41248d53cff99abc..cf9501c53febf9d80288baeb7034dd95b8aa440a 100644
--- a/Source/devtools/front_end/timeline/TimelineTreeView.js
+++ b/Source/devtools/front_end/timeline/TimelineTreeView.js
@@ -291,7 +291,12 @@ WebInspector.TimelineTreeView.eventURL = function(event)
     if (url)
         return url;
     var topFrame = event.stackTrace && event.stackTrace[0];
-    return topFrame && topFrame["url"] || null;
+    url = topFrame && topFrame["url"];
+    if (url)
+        return url;
+    var initiator = event.initiator;
+    var initiatorTopFrame = initiator && initiator.stackTrace && initiator.stackTrace[0];
+    return initiatorTopFrame && initiatorTopFrame["url"] || null;
 }
 
 /**