Introduce toSVGTextElement(), and use it

Source/core/svg/SVGTextElement.h

Index: Source/core/svg/SVGTextElement.h
diff --git a/Source/core/svg/SVGTextElement.h b/Source/core/svg/SVGTextElement.h
index 95be00e5e58eb3d14377294b1fc3922f5e2f5d4d..0ec8cbee64b2a428f63f5d2359c3a1c60b1b554e 100644
--- a/Source/core/svg/SVGTextElement.h
+++ b/Source/core/svg/SVGTextElement.h
@@ -21,6 +21,7 @@
 #ifndef SVGTextElement_h
 #define SVGTextElement_h
 
+#include "SVGNames.h"
 #include "core/svg/SVGTextPositioningElement.h"
 
 namespace WebCore {
@@ -40,6 +41,12 @@ private:
     virtual bool childShouldCreateRenderer(const NodeRenderingContext&) const;
 };
 
+inline SVGTextElement* toSVGTextElement(Node* node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(SVGNames::textTag));
+    return static_cast<SVGTextElement*>(node);
+}
+
 } // namespace WebCore
 
 #endif