Introduce toSVGSMILElement, and use it

Source/core/svg/animation/SVGSMILElement.h

 /*
  * Copyright (C) 2008 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 216 matching lines @@
 
     mutable SMILTime m_cachedDur;
     mutable SMILTime m_cachedRepeatDur;
     mutable SMILTime m_cachedRepeatCount;
     mutable SMILTime m_cachedMin;
     mutable SMILTime m_cachedMax;
 
     friend class ConditionEventListener;
 };
 
+inline SVGSMILElement* toSVGSMILElement(Element* element)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!element || SVGSMILElement::isSMILElement(element));
+    return static_cast<SVGSMILElement*>(element);
+}
+
 }
 
 #endif // SVGSMILElement_h