Add isHTMLPlugInElement() helpers for consistency with other HTML elements

Source/core/html/HTMLElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 61 matching lines @@
     bool ieForbidsInsertHTML() const;
 
     virtual HTMLFormElement* formOwner() const { return 0; }
 
     HTMLFormElement* findFormAncestor() const;
 
     bool hasDirectionAuto() const;
     TextDirection directionalityIfhasDirAutoAttribute(bool& isAuto) const;
 
     virtual bool isHTMLUnknownElement() const { return false; }
+    virtual bool isPluginElement() const { return false; }
 
     virtual bool isLabelable() const { return false; }
     // http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#interactive-content
     virtual bool isInteractiveContent() const;
     virtual void defaultEventHandler(Event*) OVERRIDE;
 
     static const AtomicString& eventNameForAttributeName(const QualifiedName& attrName);
 
     virtual bool matchesReadOnlyPseudoClass() const OVERRIDE;
     virtual bool matchesReadWritePseudoClass() const OVERRIDE;
@@ skipping 57 matching lines @@
     template<typename T> inline bool is##thisType(const PassRefPtr<T>& node) { return is##thisType(node.get()); } \
     template<typename T> inline bool is##thisType(const RefPtr<T>& node) { return is##thisType(node.get()); } \
     template <> inline bool isElementOfType<const thisType>(const HTMLElement& element) { return is##thisType(element); } \
     DEFINE_ELEMENT_TYPE_CASTS_WITH_FUNCTION(thisType)
 
 } // namespace WebCore
 
 #include "HTMLElementTypeHelpers.h"
 
 #endif // HTMLElement_h