DevTools: get rid of WebInspector.cssModel, use target models instead

LayoutTests/inspector/tracing-test.js

 function initialize_TracingTest()
 {
 
 // FIXME: remove when tracing is out of experimental
 WebInspector.inspectorView.showPanel("timeline");
-InspectorTest.tracingModel = new WebInspector.TracingModel(WebInspector.targetManager.activeTarget());
+InspectorTest.tracingModel = new WebInspector.TracingModel(WebInspector.targetManager.mainTarget());
 InspectorTest.tracingTimelineModel = new WebInspector.TracingTimelineModel(InspectorTest.tracingModel, new WebInspector.TimelineRecordHiddenTypeFilter([]));
 
 InspectorTest.invokeWithTracing = function(functionName, callback, additionalCategories)
 {
     InspectorTest.tracingTimelineModel.addEventListener(WebInspector.TimelineModel.Events.RecordingStarted, onTracingStarted, this);
     var categories = "-*,disabled-by-default-devtools.timeline*";
     if (additionalCategories)
         categories += "," + additionalCategories;
     InspectorTest.tracingTimelineModel._startRecordingWithCategories(categories);
 
@@ skipping 10 matching lines @@
     }
 
     function onTracingComplete(event)
     {
         InspectorTest.tracingTimelineModel.removeEventListener(WebInspector.TimelineModel.Events.RecordingStopped, onTracingComplete, this);
         callback();
     }
 }
 
 }