Timeline: fix screenshots for headless shell

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

Index: third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js b/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
index 4755da5ea4efecd63e412e9760476e17906bd21d..0973bec93456a38ec87d4b1ccf394ddf16e1c02f 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline_model/TimelineModel.js
@@ -635,9 +635,10 @@ WebInspector.TimelineModel.prototype = {
      */
     _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>>} */