DevTools: add Tracing agent on back-end

Source/devtools/front_end/sdk/TimelineManager.js

Index: Source/devtools/front_end/sdk/TimelineManager.js
diff --git a/Source/devtools/front_end/sdk/TimelineManager.js b/Source/devtools/front_end/sdk/TimelineManager.js
index 1ad5e7ea8133a58983e7c52e46e1203a2181f515..7aae9d87ab0d8bd3da41d4d1ed0b75122a13b631 100644
--- a/Source/devtools/front_end/sdk/TimelineManager.js
+++ b/Source/devtools/front_end/sdk/TimelineManager.js
@@ -39,7 +39,7 @@ WebInspector.TimelineManager = function(target)
     this._dispatcher = new WebInspector.TimelineDispatcher(this);
     this._enablementCount = 0;
     this._jsProfilerStarted = false;
-    TimelineAgent.enable(WebInspector.experimentsSettings.timelineTracingMode.isEnabled() ? WebInspector.TimelineManager.defaultTracingCategories : "");
+    TimelineAgent.enable();
 }
 
 WebInspector.TimelineManager.EventTypes = {
@@ -49,8 +49,6 @@ WebInspector.TimelineManager.EventTypes = {
     TimelineProgress: "TimelineProgress"
 }
 
-WebInspector.TimelineManager.defaultTracingCategories = "*,disabled-by-default-cc.debug,disabled-by-default-devtools.timeline";
-
 WebInspector.TimelineManager.prototype = {
     /**
      * @return {boolean}