Use DEFINE_NODE_TYPE_CASTS instead of using manual toHTMLFooElement()

Source/core/html/HTMLBodyElement.h

Index: Source/core/html/HTMLBodyElement.h
diff --git a/Source/core/html/HTMLBodyElement.h b/Source/core/html/HTMLBodyElement.h
index fd1a960d37cfe9d95b9b80ac44bf5111e4767901..987ffbf6fd50de93d36178f28af9ca820bf391fe 100644
--- a/Source/core/html/HTMLBodyElement.h
+++ b/Source/core/html/HTMLBodyElement.h
@@ -92,11 +92,7 @@ private:
     virtual void addSubresourceAttributeURLs(ListHashSet<KURL>&) const;
 };
 
-inline HTMLBodyElement* toHTMLBodyElement(Node* node)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!node || node->hasTagName(HTMLNames::bodyTag));
-    return static_cast<HTMLBodyElement*>(node);
-}
+DEFINE_NODE_TYPE_CASTS(HTMLBodyElement, hasTagName(HTMLNames::bodyTag));
 
 } //namespace