DevTools: [Timeline] do not collect "devtools" category because we do not use it any more.

Source/devtools/front_end/timeline/TracingTimelineModel.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
  * @param {!WebInspector.TracingModel} tracingModel
  * @param {!WebInspector.TimelineModel.Filter} recordFilter
  * @extends {WebInspector.TimelineModel}
  */
@@ skipping 92 matching lines @@
      * @param {boolean} captureStacks
      * @param {boolean} captureMemory
      * @param {boolean} capturePictures
      */
     startRecording: function(captureStacks, captureMemory, capturePictures)
     {
         var categories;
         if (WebInspector.experimentsSettings.timelineTracingMode.isEnabled()) {
             categories = WebInspector.TracingTimelineModel.defaultTracingCategoryFilter;
         } else {
-            var categoriesArray = ["disabled-by-default-devtools.timeline", "disabled-by-default-devtools.timeline.frame", "devtools"];
+            var categoriesArray = ["disabled-by-default-devtools.timeline", "disabled-by-default-devtools.timeline.frame"];
             if (captureStacks)
                 categoriesArray.push("disabled-by-default-devtools.timeline.stack");
             if (capturePictures)
                 categoriesArray.push("disabled-by-default-devtools.timeline.layers", "disabled-by-default-devtools.timeline.picture");
             categories = categoriesArray.join(",");
         }
         this._startRecordingWithCategories(categories);
     },
 
     stopRecording: function()
@@ skipping 528 matching lines @@
      * @param {!WebInspector.TracingTimelineModel.TraceEventRecord} child
      */
     _addChild: function(child)
     {
         this._children.push(child);
         child.parent = this;
     },
 
 
 }