DevTools: move session logic from TracingModel to TimelineModel

LayoutTests/inspector/tracing/worker-events.html

Index: LayoutTests/inspector/tracing/worker-events.html
diff --git a/LayoutTests/inspector/tracing/worker-events.html b/LayoutTests/inspector/tracing/worker-events.html
index 23de85cd17b71a04d435cf9b24c3533d6412f8df..688aac5eab278de8a09a56c6cedea64fc7a21fca 100644
--- a/LayoutTests/inspector/tracing/worker-events.html
+++ b/LayoutTests/inspector/tracing/worker-events.html
@@ -55,11 +55,11 @@ function test()
 
     function processEvent(event)
     {
-        if (!event.hasCategory(WebInspector.TracingModel.DevToolsMetadataEventCategory) || event.name !== WebInspector.TracingModel.DevToolsMetadataEvent.TracingSessionIdForWorker)
+        if (!event.hasCategory(WebInspector.TracingModel.DevToolsMetadataEventCategory) || event.name !== WebInspector.TimelineModel.DevToolsMetadataEvent.TracingSessionIdForWorker)
             return;
 
         ++workerMetadataEventCount;
-        InspectorTest.assertEquals(InspectorTest.tracingModel().sessionId(), event.args["data"]["sessionId"]);
+        InspectorTest.assertEquals(InspectorTest.tracingTimelineModel().sessionId(), event.args["data"]["sessionId"]);
         InspectorTest.addResult("Got DevTools worker metadata event(" + workerMetadataEventCount +  "): " + event.name);
     }