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

Source/devtools/front_end/TimelineView.js

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
@@ skipping 1013 matching lines @@
             this._dataElement.createTextChild(WebInspector.UIString("× %d", presentationRecord.presentationChildren().length));
         } else {
             var detailsNode = WebInspector.TimelineUIUtils.buildDetailsNode(record, this._linkifier);
             if (detailsNode) {
                 this._dataElement.appendChild(document.createTextNode("("));
                 this._dataElement.appendChild(detailsNode);
                 this._dataElement.appendChild(document.createTextNode(")"));
             }
         }
 
-        this._expandArrowElement.classList.toggle("parent", presentationRecord.hasPresentationChildren());
+        this._expandArrowElement.classList.toggle("parent", presentationRecord.expandable());
         this._expandArrowElement.classList.toggle("expanded", !!presentationRecord.visibleChildrenCount());
         this._record.setListRow(this);
     },
 
     highlight: function(regExp, domChanges)
     {
         var matchInfo = this.element.textContent.match(regExp);
         if (matchInfo)
             WebInspector.highlightSearchResult(this.element, matchInfo.index, matchInfo[0].length, domChanges);
     },
@@ skipping 199 matching lines @@
             this._element.classList.remove("hidden");
         } else
             this._element.classList.add("hidden");
     },
 
     _dispose: function()
     {
         this._element.remove();
     }
 }