Make sure the root node of selector queries is a ContainerNode

Source/web/WebNode.cpp

 /*
  * Copyright (C) 2009 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 183 matching lines @@
 WebNodeList WebNode::getElementsByTagName(const WebString& tag) const
 {
     if (m_private->isContainerNode())
         return WebNodeList(toContainerNode(m_private.get())->getElementsByTagName(tag));
     return WebNodeList(EmptyNodeList::create(m_private.get()));
 }
 
 WebElement WebNode::querySelector(const WebString& tag, WebExceptionCode& ec) const
 {
     TrackExceptionState exceptionState;
-    WebElement element(m_private->querySelector(tag, exceptionState));
+    WebElement element;
+    if (m_private->isContainerNode())
+        element = toContainerNode(m_private.get())->querySelector(tag, exceptionState);
     ec = exceptionState.code();
     return element;
 }
 
 WebElement WebNode::rootEditableElement() const
 {
     return WebElement(m_private->rootEditableElement());
 }
 
 bool WebNode::focused() const
@@ skipping 48 matching lines @@
     m_private = node;
     return *this;
 }
 
 WebNode::operator PassRefPtr<Node>() const
 {
     return m_private.get();
 }
 
 } // namespace blink