DevTools: Get rid of Element.prototype.enableStyleClass

Source/devtools/front_end/LayerTree.js

 /*
  * Copyright (C) 2013 Google 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 205 matching lines @@
     {
         this._layerTree._selectedNodeChanged(this);
         return false;
     },
 
     /**
      * @param {boolean} hovered
      */
     setHovered: function(hovered)
     {
-        this.listItemElement.enableStyleClass("hovered", hovered);
+        this.listItemElement.classList.toggle("hovered", hovered);
     },
 
     __proto__: TreeElement.prototype
 }