DevTools: Use proper target when processing worker thread events.

third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineProfileTree.js

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 WebInspector.TimelineProfileTree = { };
 
 /**
  * @constructor
  */
 WebInspector.TimelineProfileTree.Node = function()
@@ skipping 185 matching lines @@
         var url = frame["url"];
         if (url)
             return url;
         frame = frame.parent;
     }
     return null;
 }
 
 /**
  * @param {!WebInspector.TracingModel.Event} event
- * @return {?Object}
+ * @return {?RuntimeAgent.CallFrame}
  */
 WebInspector.TimelineProfileTree.eventStackFrame = function(event)
 {
     if (event.name === WebInspector.TimelineModel.RecordType.JSFrame)
-        return event.args["data"];
+        return /** @type {?RuntimeAgent.CallFrame} */ (event.args["data"] || null);
     var topFrame = event.stackTrace && event.stackTrace[0];
     if (topFrame)
-        return topFrame;
+        return /** @type {!RuntimeAgent.CallFrame} */ (topFrame);
     var initiator = event.initiator;
-    return initiator && initiator.stackTrace && initiator.stackTrace[0] || null;
+    return /** @type {?RuntimeAgent.CallFrame} */ (initiator && initiator.stackTrace && initiator.stackTrace[0] || null);
 }
 
 /**
  * @constructor
  * @param {function(!WebInspector.TracingModel.Event):string} titleMapper
  * @param {function(!WebInspector.TracingModel.Event):string} categoryMapper
  */
 WebInspector.TimelineAggregator = function(titleMapper, categoryMapper)
 {
     this._titleMapper = titleMapper;
@@ skipping 143 matching lines @@
      * @param {function(!WebInspector.TimelineProfileTree.Node):string} nodeToGroupId
      * @param {!WebInspector.TimelineProfileTree.Node} node
      * @return {!WebInspector.TimelineProfileTree.Node}
      */
     _nodeToGroupNode: function(nodeToGroupId, node)
     {
         var id = nodeToGroupId(node);
         return this._groupNodes.get(id) || this._buildGroupNode(id, node.event);
     },
 }