Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderScrollbarPart.h

Index: Source/core/rendering/RenderScrollbarPart.h
diff --git a/Source/core/rendering/RenderScrollbarPart.h b/Source/core/rendering/RenderScrollbarPart.h
index b81e638d776b4e87b10c0f16a48769a681be193b..a1f24654f4b80e0fd54239f946866203b487022d 100644
--- a/Source/core/rendering/RenderScrollbarPart.h
+++ b/Source/core/rendering/RenderScrollbarPart.h
@@ -78,20 +78,7 @@ private:
     ScrollbarPart m_part;
 };
 
-inline RenderScrollbarPart* toRenderScrollbarPart(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderScrollbarPart());
-    return static_cast<RenderScrollbarPart*>(object);
-}
-
-inline const RenderScrollbarPart* toRenderScrollbarPart(const RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderScrollbarPart());
-    return static_cast<const RenderScrollbarPart*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderScrollbarPart(const RenderScrollbarPart*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderScrollbarPart, isRenderScrollbarPart());
 
 } // namespace WebCore