Timeline: fix screenshots for headless shell

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

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 617 matching lines @@
         this._mainThreadEvents.splice(this._mainThreadEvents.lowerBound(firstPaintEvent, WebInspector.TracingModel.Event.compareStartTime), 0, firstPaintEvent);
         var firstPaintRecord = new WebInspector.TimelineModel.Record(firstPaintEvent);
         this._eventDividerRecords.splice(this._eventDividerRecords.lowerBound(firstPaintRecord, WebInspector.TimelineModel.Record._compareStartTime), 0, firstPaintRecord);
     },
 
     /**
      * @param {!WebInspector.TracingModel} tracingModel
      */
     _processBrowserEvents: function(tracingModel)
     {
-        var browserMain = tracingModel.threadByName("Browser", "CrBrowserMain");
+        var browserMain = WebInspector.TracingModel.browserMainThread(tracingModel);
         if (!browserMain)
             return;
+
         // Disregard regular events, we don't need them yet, but still process to get proper metadata.
         browserMain.events().forEach(this._processBrowserEvent, this);
         /** @type {!Map<!WebInspector.TimelineModel.AsyncEventGroup, !Array<!WebInspector.TracingModel.AsyncEvent>>} */
         var asyncEventsByGroup = new Map();
         this._processAsyncEvents(asyncEventsByGroup, browserMain.asyncEvents());
         this._mergeAsyncEvents(this._mainThreadAsyncEventsByGroup, asyncEventsByGroup);
     },
 
     _buildTimelineRecords: function()
     {
@@ skipping 1136 matching lines @@
         if (!id)
             return;
         /** @type {!Map<string, !WebInspector.TracingModel.Event>|undefined} */
         var initiatorMap = this._initiatorByType.get(initiatorType);
         if (isInitiator)
             initiatorMap.set(id, event);
         else
             event.initiator = initiatorMap.get(id) || null;
     }
 }