DevTools: use target-based model accessors only.

Source/devtools/front_end/timeline/CountersGraph.js

Index: Source/devtools/front_end/timeline/CountersGraph.js
diff --git a/Source/devtools/front_end/timeline/CountersGraph.js b/Source/devtools/front_end/timeline/CountersGraph.js
index d135e7e1e5008b9d01ae9b8bbc02bacd27db1a19..3fe10baea57ee1ed36d85cacd57986c57e92bc66 100644
--- a/Source/devtools/front_end/timeline/CountersGraph.js
+++ b/Source/devtools/front_end/timeline/CountersGraph.js
@@ -74,6 +74,14 @@ WebInspector.CountersGraph = function(title, delegate, model)
 }
 
 WebInspector.CountersGraph.prototype = {
+    /**
+     * @return {?WebInspector.Target}
+     */
+    target: function()
+    {
+        return this._model.target();
+    },
+
     _createCurrentValuesBar: function()
     {
         this._currentValuesBar = this._graphsContainer.element.createChild("div");