DevTools: Support timeline JS sampling for all threads.

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
  */
 WebInspector.TracingModel = function()
@@ skipping 790 matching lines @@
     this._stack = [];
 }
 
 WebInspector.TracingModel.Thread.prototype = {
     /**
      * @return {?WebInspector.Target}
      */
     target: function()
     {
         //FIXME: correctly specify target
-        return WebInspector.targetManager.targets()[0] || null;
+        if (this.name() === "CrRendererMain")
+            return WebInspector.targetManager.targets()[0] || null;
+        else
+            return null;
     },
 
     /**
      * @param {!WebInspector.TracingManager.EventPayload} payload
      * @return {?WebInspector.TracingModel.Event} event
      */
     _addEvent: function(payload)
     {
         var timestamp = payload.ts / 1000;
         if (payload.ph === WebInspector.TracingModel.Phase.End) {
@@ skipping 53 matching lines @@
     /**
      * @return {!Array.<!WebInspector.TracingModel.Event>}
      */
     asyncEvents: function()
     {
         return this._asyncEvents;
     },
 
     __proto__: WebInspector.TracingModel.NamedObject.prototype
 }