Introduce DEFINE_RENDER_OBJECT_TYPE_CASTS to replace manual toRenderFoo, and use it

Source/core/rendering/RenderFlexibleBox.h

Index: Source/core/rendering/RenderFlexibleBox.h
diff --git a/Source/core/rendering/RenderFlexibleBox.h b/Source/core/rendering/RenderFlexibleBox.h
index f82a44579a494d82231c772056becae8f047cb1f..c9297da700160bb01b34e33c3df3c98e64f3e7ef 100644
--- a/Source/core/rendering/RenderFlexibleBox.h
+++ b/Source/core/rendering/RenderFlexibleBox.h
@@ -161,20 +161,7 @@ private:
     int m_numberOfInFlowChildrenOnFirstLine;
 };
 
-inline RenderFlexibleBox* toRenderFlexibleBox(RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isFlexibleBox());
-    return static_cast<RenderFlexibleBox*>(object);
-}
-
-inline const RenderFlexibleBox* toRenderFlexibleBox(const RenderObject* object)
-{
-    ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isFlexibleBox());
-    return static_cast<const RenderFlexibleBox*>(object);
-}
-
-// This will catch anyone doing an unnecessary cast.
-void toRenderFlexibleBox(const RenderFlexibleBox*);
+DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderFlexibleBox, isFlexibleBox());
 
 } // namespace WebCore