Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderFlowThread.h

Index: Source/core/rendering/RenderFlowThread.h
diff --git a/Source/core/rendering/RenderFlowThread.h b/Source/core/rendering/RenderFlowThread.h
index c6106041319b259626fd4f587a466cf5d3998d98..4f1e3faf5a3c054b643b0a81fcde6a95a84a3cea 100644
--- a/Source/core/rendering/RenderFlowThread.h
+++ b/Source/core/rendering/RenderFlowThread.h
@@ -291,20 +291,7 @@ private:
 
 };
 
-inline RenderFlowThread* toRenderFlowThread(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderFlowThread());
-    return static_cast<RenderFlowThread*>(object);
-}
-
-inline const RenderFlowThread* toRenderFlowThread(const RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderFlowThread());
-    return static_cast<const RenderFlowThread*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderFlowThread(const RenderFlowThread*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderFlowThread, isRenderFlowThread());
 
 class CurrentRenderFlowThreadMaintainer {
     WTF_MAKE_NONCOPYABLE(CurrentRenderFlowThreadMaintainer);