iframes with allowpaymentrequest attribute are allowed to make payment requests.

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 10 matching lines @@
  *
  */
 
 #ifndef HTMLIFrameElement_h
 #define HTMLIFrameElement_h
 
 #include "core/CoreExport.h"
 #include "core/html/HTMLFrameElementBase.h"
 #include "core/html/HTMLIFrameElementPermissions.h"
 #include "core/html/HTMLIFrameElementSandbox.h"
+#include "platform/Supplementable.h"
 #include "public/platform/WebVector.h"
 #include "public/platform/modules/permissions/WebPermissionType.h"
 
 namespace blink {
 
-class CORE_EXPORT HTMLIFrameElement final : public HTMLFrameElementBase {
+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();
   ~HTMLIFrameElement() override;
   DOMTokenList* sandbox() const;
   DOMTokenList* permissions() const;
 
   void sandboxValueWasSet();
   void permissionsValueWasSet();
@@ skipping 41 matching lines @@
   Member<HTMLIFrameElementPermissions> m_permissions;
 
   WebVector<WebPermissionType> m_delegatedPermissions;
 
   ReferrerPolicy m_referrerPolicy;
 };
 
 }  // namespace blink
 
 #endif  // HTMLIFrameElement_h