Introduce toSVGMaskElement(), and use it

Source/core/svg/SVGMaskElement.h

 /*
  * Copyright (C) 2005 Alexander Kellett <lypanov@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 #ifndef SVGMaskElement_h
 #define SVGMaskElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGAnimatedBoolean.h"
 #include "core/svg/SVGAnimatedEnumeration.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGElement.h"
 #include "core/svg/SVGExternalResourcesRequired.h"
 #include "core/svg/SVGTests.h"
 #include "core/svg/SVGUnitTypes.h"
 
 namespace WebCore {
 
@@ skipping 28 matching lines @@
         DECLARE_ANIMATED_LENGTH(Height, height)
         DECLARE_ANIMATED_BOOLEAN(ExternalResourcesRequired, externalResourcesRequired)
     END_DECLARE_ANIMATED_PROPERTIES
 
     // SVGTests
     virtual void synchronizeRequiredFeatures() { SVGTests::synchronizeRequiredFeatures(this); }
     virtual void synchronizeRequiredExtensions() { SVGTests::synchronizeRequiredExtensions(this); }
     virtual void synchronizeSystemLanguage() { SVGTests::synchronizeSystemLanguage(this); }
 };
 
+inline SVGMaskElement* toSVGMaskElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::maskTag));
+    return static_cast<SVGMaskElement*>(node);
+}
+
 }
 
 #endif