Timeline: fix expansion arrow appearing on rows with no visible children

Source/devtools/front_end/TimelinePresentationModel.js

Index: Source/devtools/front_end/TimelinePresentationModel.js
diff --git a/Source/devtools/front_end/TimelinePresentationModel.js b/Source/devtools/front_end/TimelinePresentationModel.js
index 2c44db69b1d7a62aa01f3ac229675b35f7df563c..c07a50e94d1e1e3e59159c36a87a607bb20792e0 100644
--- a/Source/devtools/front_end/TimelinePresentationModel.js
+++ b/Source/devtools/front_end/TimelinePresentationModel.js
@@ -346,14 +346,6 @@ WebInspector.TimelinePresentationModel.Record.prototype = {
     /**
      * @return {boolean}
      */
-    hasPresentationChildren: function()
-    {
-        return !!this._presentationChildren.length;
-    },
-
-    /**
-     * @return {boolean}
-     */
     coalesced: function()
     {
         return this._coalesced;