Timeline: do not imply event.thread.target is the main target

Source/devtools/front_end/sdk/TracingManager.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.Object}
  * @implements {WebInspector.TargetManager.Observer}
@@ skipping 44 matching lines @@
      * @param {!WebInspector.Target} target
      */
     targetRemoved: function(target)
     {
         if (this._target !== target)
             return;
         delete this._target;
     },
 
     /**
+     * @return {?WebInspector.Target}
+     */
+    target: function()
+    {
+        return this._target;
+    },
+
+    /**
      * @param {number} usage
      */
     _bufferUsage: function(usage)
     {
         this.dispatchEventToListeners(WebInspector.TracingManager.Events.BufferUsage, usage);
     },
 
     /**
      * @param {!Array.<!WebInspector.TracingManager.EventPayload>} events
      */
@@ skipping 67 matching lines @@
     dataCollected: function(data)
     {
         this._tracingManager._eventsCollected(data);
     },
 
     tracingComplete: function()
     {
         this._tracingManager._tracingComplete();
     }
 }