Don't expose WebKitShadowRoot constructor.

LayoutTests/fast/dom/shadow/resources/shadow-dom.js

 function createShadowRoot()
 {
     var children = Array.prototype.slice.call(arguments);
     if ((children[0] instanceof Object) && !(children[0] instanceof Node))
         return {'isShadowRoot': true,
                 'attributes': children[0],
                 'children': children.slice(1)};
     return {'isShadowRoot': true,
             'children': children};
 }
@@ skipping 23 matching lines @@
     return element;
 }
 
 function isShadowHost(node)
 {
     return window.internals.oldestShadowRoot(node);
 }
 
 function isShadowRoot(node)
 {
-    return node instanceof window.WebKitShadowRoot;
+    return node instanceof window.ShadowRoot;
 }
 
 function isIframeElement(element)
 {
     return element && element.nodeName == 'IFRAME';
 }
 
 // You can spefify youngerShadowRoot by consecutive slashes.
 // See LayoutTests/fast/dom/shadow/get-element-by-id-in-shadow-root.html for actual usages.
 function getNodeInTreeOfTrees(path)
@@ skipping 175 matching lines @@
     debug('Traverse in backward.');
     showComposedShadowTreeByTraversingInBackward(node);
 
     debug('');
 }
 
 function showNextNode(node) {
     var next = internals.nextNodeByWalker(node);
     debug('Next node of [' + dumpNode(node) + '] is [' + dumpNode(next) + ']');
 }