Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderFieldset.h

Index: Source/core/rendering/RenderFieldset.h
diff --git a/Source/core/rendering/RenderFieldset.h b/Source/core/rendering/RenderFieldset.h
index 65329bd692370179982576bb1fa82abf5108442c..944ab4c1dc694ce7bf1e52c34449ff162e01412c 100644
--- a/Source/core/rendering/RenderFieldset.h
+++ b/Source/core/rendering/RenderFieldset.h
@@ -50,14 +50,7 @@ private:
     virtual void paintMask(PaintInfo&, const LayoutPoint&);
 };
 
-inline RenderFieldset* toRenderFieldset(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isFieldset());
-    return static_cast<RenderFieldset*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderFieldset(const RenderFieldset*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderFieldset, isFieldset());
 
 } // namespace WebCore