iframes with allowpaymentrequest attribute are allowed to make payment requests.

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

Index: third_party/WebKit/Source/core/html/HTMLIFrameElement.h
diff --git a/third_party/WebKit/Source/core/html/HTMLIFrameElement.h b/third_party/WebKit/Source/core/html/HTMLIFrameElement.h
index a580503b4716835019bfe59a8c945432cdd87395..b039b1f82d2284b88f49304711d313430dfc0d5f 100644
--- a/third_party/WebKit/Source/core/html/HTMLIFrameElement.h
+++ b/third_party/WebKit/Source/core/html/HTMLIFrameElement.h
@@ -73,6 +73,8 @@ class CORE_EXPORT HTMLIFrameElement final : public HTMLFrameElementBase {
 
   bool allowFullscreen() const override { return m_allowFullscreen; }
 
+  bool allowPaymentRequest() const override { return m_allowPaymentRequest; }
+
   const WebVector<WebPermissionType>& delegatedPermissions() const override {
     return m_delegatedPermissions;
   }
@@ -83,6 +85,7 @@ class CORE_EXPORT HTMLIFrameElement final : public HTMLFrameElementBase {
   AtomicString m_csp;
   bool m_didLoadNonEmptyDocument;
   bool m_allowFullscreen;
+  bool m_allowPaymentRequest;
   Member<HTMLIFrameElementSandbox> m_sandbox;
   Member<HTMLIFrameElementPermissions> m_permissions;