DevTools: move session logic from TracingModel to TimelineModel

Source/devtools/front_end/timeline/TimelinePanel.js

Index: Source/devtools/front_end/timeline/TimelinePanel.js
diff --git a/Source/devtools/front_end/timeline/TimelinePanel.js b/Source/devtools/front_end/timeline/TimelinePanel.js
index c647bd7fa1fdd2a16f56a388682da16258207737..cc9e4d20f1cb1e4032e7f3d5e48bbc26f9080de7 100644
--- a/Source/devtools/front_end/timeline/TimelinePanel.js
+++ b/Source/devtools/front_end/timeline/TimelinePanel.js
@@ -242,7 +242,7 @@ WebInspector.TimelinePanel.prototype = {
     {
         if (!this._lazyFrameModel) {
             var tracingFrameModel = new WebInspector.TracingTimelineFrameModel();
-            tracingFrameModel.addTraceEvents(this._model.target(), this._model.inspectedTargetEvents(), this._tracingModel.sessionId() || "");
+            tracingFrameModel.addTraceEvents(this._model.target(), this._model.inspectedTargetEvents(), this._model.sessionId() || "");
             this._lazyFrameModel = tracingFrameModel;
         }
         return this._lazyFrameModel;
@@ -856,7 +856,7 @@ WebInspector.TimelinePanel.prototype = {
         this._updateToggleTimelineButton(false);
         if (this._lazyFrameModel) {
             this._lazyFrameModel.reset();
-            this._lazyFrameModel.addTraceEvents(this._model.target(), this._model.inspectedTargetEvents(), this._tracingModel.sessionId());
+            this._lazyFrameModel.addTraceEvents(this._model.target(), this._model.inspectedTargetEvents(), this._model.sessionId());
         }
         this._overviewPane.reset();
         this._overviewPane.setBounds(this._model.minimumRecordTime(), this._model.maximumRecordTime());