Introduce toSVGGlyphElement(), toSVGHKernElement() and toSVGVKernElement(), and use them

Source/core/svg/SVGHKernElement.h

Index: Source/core/svg/SVGHKernElement.h
diff --git a/Source/core/svg/SVGHKernElement.h b/Source/core/svg/SVGHKernElement.h
index c142d95579fb411efebaf9c28ecc6a7c2769d647..74b158776a322cd5bc0fd2d964fe62c19c668baf 100644
--- a/Source/core/svg/SVGHKernElement.h
+++ b/Source/core/svg/SVGHKernElement.h
@@ -23,6 +23,7 @@
 #define SVGHKernElement_h
 
 #if ENABLE(SVG_FONTS)
+#include "SVGNames.h"
 #include "core/svg/SVGFontElement.h"
 
 namespace WebCore {
@@ -42,6 +43,12 @@ private:
     virtual bool rendererIsNeeded(const NodeRenderingContext&) { return false; }
 };
 
+inline SVGHKernElement* toSVGHKernElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::hkernTag));
+    return static_cast<SVGHKernElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif // ENABLE(SVG_FONTS)