Use new is*Element() helper functions further more in HTML code

Source/core/html/HTMLTablePartElement.cpp

 /**
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 68 matching lines @@
     } else if (name == heightAttr) {
         if (!value.isEmpty())
             addHTMLLengthToStyle(style, CSSPropertyHeight, value);
     } else
         HTMLElement::collectStyleForPresentationAttribute(name, value, style);
 }
 
 HTMLTableElement* HTMLTablePartElement::findParentTable() const
 {
     ContainerNode* parent = NodeRenderingTraversal::parent(this);
-    while (parent && !parent->hasTagName(tableTag))
+    while (parent && !isHTMLTableElement(*parent))
         parent = NodeRenderingTraversal::parent(parent);
     return toHTMLTableElement(parent);
 }
 
 }