Record DevTools metadata events on worker threads when starting recoring tracing based Timeline

Source/devtools/front_end/timeline/TracingModel.js

 /*
  * Copyright 2014 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.
  */
 
 /**
  * @constructor
  * @extends {WebInspector.SDKObject}
  */
@@ skipping 56 matching lines @@
     ThreadSortIndex: "thread_sort_index",
     ThreadName: "thread_name"
 }
 
 WebInspector.TracingModel.DevToolsMetadataEventCategory = "disabled-by-default-devtools.timeline";
 
 WebInspector.TracingModel.FrameLifecycleEventCategory = "cc,devtools";
 
 WebInspector.TracingModel.DevToolsMetadataEvent = {
     TracingStartedInPage: "TracingStartedInPage",
+    TracingStartedInWorker: "TracingStartedInWorker",
 };
 
 WebInspector.TracingModel.prototype = {
     /**
      * @return {!Array.<!WebInspector.TracingModel.Event>}
      */
     devtoolsMetadataEvents: function()
     {
         return this._devtoolsMetadataEvents;
     },
@@ skipping 575 matching lines @@
     started: function(consoleTimeline, sessionId)
     {
         this._tracingModel._tracingStarted(sessionId);
     },
 
     stopped: function()
     {
         this._tracingModel._onStop();
     }
 }