KEYGEN elements should always create LayoutBlockFlow, regardless of display type.

Source/core/html/HTMLKeygenElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 19 matching lines @@
 
 class HTMLSelectElement;
 
 class HTMLKeygenElement final : public HTMLFormControlElementWithState {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<HTMLKeygenElement> create(Document&, HTMLFormElement*);
 
     virtual bool willValidate() const override { return false; }
 
+    virtual LayoutObject* createLayoutObject(const LayoutStyle&) override;
+
 private:
     HTMLKeygenElement(Document&, HTMLFormElement*);
 
     virtual bool areAuthorShadowsAllowed() const override { return false; }
 
     virtual bool canStartSelection() const override { return false; }
 
     virtual void parseAttribute(const QualifiedName&, const AtomicString&) override;
 
     virtual bool appendFormData(FormDataList&, bool) override;
     virtual const AtomicString& formControlType() const override;
     virtual bool isOptionalFormControl() const override { return false; }
 
     virtual bool isEnumeratable() const override { return true; }
     virtual bool isInteractiveContent() const override;
     virtual bool supportsAutofocus() const override;
     virtual bool supportLabels() const override { return true; }
 
     virtual void resetImpl() override;
     virtual bool shouldSaveAndRestoreFormControlState() const override { return false; }
 
     virtual void didAddClosedShadowRoot(ShadowRoot&) override;
 
     HTMLSelectElement* shadowSelect() const;
 };
 
 } // namespace blink
 
 #endif // HTMLKeygenElement_h