Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/svg/RenderSVGGradientStop.h

Index: Source/core/rendering/svg/RenderSVGGradientStop.h
diff --git a/Source/core/rendering/svg/RenderSVGGradientStop.h b/Source/core/rendering/svg/RenderSVGGradientStop.h
index bf2a10aabe83ca2a1522de34ce67c0a3fa47bc6f..e56274e3ffceab15cbc7f72e3100df558535af83 100644
--- a/Source/core/rendering/svg/RenderSVGGradientStop.h
+++ b/Source/core/rendering/svg/RenderSVGGradientStop.h
@@ -54,11 +54,7 @@ private:
     SVGGradientElement* gradientElement() const;
 };
 
-inline const RenderSVGGradientStop* toRenderSVGGradientStop(const RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isSVGGradientStop());
-    return static_cast<const RenderSVGGradientStop*>(object);
-}
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderSVGGradientStop, isSVGGradientStop());
 
 }