Timeline: produce session cookie when timeline is started

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..9be7603a0d77178047a7dcff49c3a8b674f3d53c 100644
--- a/Source/devtools/front_end/TimelineManager.js
+++ b/Source/devtools/front_end/TimelineManager.js
@@ -38,6 +38,7 @@ WebInspector.TimelineManager = function(target)
     WebInspector.TargetAwareObject.call(this, target);
     this._dispatcher = new WebInspector.TimelineDispatcher(this);
     this._enablementCount = 0;
+    this._sessionId = "";
     TimelineAgent.enable(WebInspector.experimentsSettings.timelineTracingMode.isEnabled() ? WebInspector.TimelineManager.defaultTracingCategories : "");
 }
 
@@ -127,6 +128,14 @@ WebInspector.TimelineManager.prototype = {
     },
 
     /**
+     * @return {string}
+     */
+    sessionId: function()
+    {
+        return this._sessionId;
+    },
+
+    /**
      * @param {function(?Protocol.Error)|undefined} callback
      * @param {?Protocol.Error} error
      * @param {!Array.<!TimelineAgent.TimelineEvent>=} events
@@ -183,15 +192,17 @@ WebInspector.TimelineDispatcher.prototype = {
     },
 
     /**
+     * @param {string} sessionId
      * @param {boolean=} consoleTimeline
      */
-    started: function(consoleTimeline)
+    started: function(sessionId, consoleTimeline)
     {
         if (consoleTimeline) {
             // Wake up timeline panel module.
             WebInspector.moduleManager.loadModule("timeline");
         }
         this._started = true;
+        this._manager._sessionId = sessionId;
         this._manager.dispatchEventToListeners(WebInspector.TimelineManager.EventTypes.TimelineStarted, consoleTimeline);
     },