Experiment with blocking script inside fragment-parser-inserted `<iframe srcdoc>`.

third_party/WebKit/Source/core/html/HTMLIFrameElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Simon Hausmann <hausmann@kde.org>
  * Copyright (C) 2004, 2006, 2008, 2009 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 23 matching lines @@
 
 namespace blink {
 
 class CORE_EXPORT HTMLIFrameElement final
     : public HTMLFrameElementBase,
       public Supplementable<HTMLIFrameElement> {
   DEFINE_WRAPPERTYPEINFO();
   USING_GARBAGE_COLLECTED_MIXIN(HTMLIFrameElement);
 
  public:
-  DECLARE_NODE_FACTORY(HTMLIFrameElement);
   DECLARE_VIRTUAL_TRACE();
+
+  static HTMLIFrameElement* create(Document&, bool createdByFragmentParser);
   ~HTMLIFrameElement() override;
   DOMTokenList* sandbox() const;
   DOMTokenList* permissions() const;
+  bool createdByFragmentParser() const { return m_createdByFragmentParser; }
 
   void sandboxValueWasSet();
   void permissionsValueWasSet();
 
  private:
-  explicit HTMLIFrameElement(Document&);
+  HTMLIFrameElement(Document&, bool createdByFragmentParser);
 
   void parseAttribute(const AttributeModificationParams&) override;
   bool isPresentationAttribute(const QualifiedName&) const override;
   void collectStyleForPresentationAttribute(const QualifiedName&,
                                             const AtomicString&,
                                             MutableStylePropertySet*) override;
 
   InsertionNotificationRequest insertedInto(ContainerNode*) override;
   void removedFrom(ContainerNode*) override;
 
@@ skipping 16 matching lines @@
     return m_delegatedPermissions;
   }
 
   bool initializePermissionsAttribute();
 
   AtomicString m_name;
   AtomicString m_csp;
   bool m_didLoadNonEmptyDocument;
   bool m_allowFullscreen;
   bool m_allowPaymentRequest;
+  const bool m_createdByFragmentParser;
   Member<HTMLIFrameElementSandbox> m_sandbox;
   Member<HTMLIFrameElementPermissions> m_permissions;
 
   WebVector<WebPermissionType> m_delegatedPermissions;
 
   ReferrerPolicy m_referrerPolicy;
 };
 
 }  // namespace blink
 
 #endif  // HTMLIFrameElement_h