DevTools: add Tracing agent on back-end

Source/devtools/front_end/TimelineManager.js

Index: Source/devtools/front_end/TimelineManager.js
diff --git a/Source/devtools/front_end/TimelineManager.js b/Source/devtools/front_end/TimelineManager.js
index 2a346c1d6c0c3f88a956989c8e2a80f0e32f1c5f..6b57bfff95df443832ab8687b7026ba901ade5b5 100644
--- a/Source/devtools/front_end/TimelineManager.js
+++ b/Source/devtools/front_end/TimelineManager.js
@@ -38,7 +38,7 @@ WebInspector.TimelineManager = function(target)
     WebInspector.TargetAwareObject.call(this, target);
     this._dispatcher = new WebInspector.TimelineDispatcher(this);
     this._enablementCount = 0;
-    TimelineAgent.enable(WebInspector.experimentsSettings.timelineTracingMode.isEnabled() ? WebInspector.TimelineManager.defaultTracingCategories : "");
+    TimelineAgent.enable();
 }
 
 WebInspector.TimelineManager.EventTypes = {
@@ -48,8 +48,6 @@ WebInspector.TimelineManager.EventTypes = {
     TimelineProgress: "TimelineProgress"
 }
 
-WebInspector.TimelineManager.defaultTracingCategories = "*,disabled-by-default-cc.debug,disabled-by-default-devtools.timeline";
-
 WebInspector.TimelineManager.prototype = {
     /**
      * @return {boolean}