iframes with allowpaymentrequest attribute are allowed to make payment requests.

third_party/WebKit/Source/core/frame/FrameOwner.h

Index: third_party/WebKit/Source/core/frame/FrameOwner.h
diff --git a/third_party/WebKit/Source/core/frame/FrameOwner.h b/third_party/WebKit/Source/core/frame/FrameOwner.h
index 6a3e23bef5fefa93a887c6efe7b50c80cb28989d..6eb2a2f740874618040d127737bc274d96e3bbc6 100644
--- a/third_party/WebKit/Source/core/frame/FrameOwner.h
+++ b/third_party/WebKit/Source/core/frame/FrameOwner.h
@@ -41,6 +41,7 @@ class CORE_EXPORT FrameOwner : public GarbageCollectedMixin {
   virtual int marginWidth() const = 0;
   virtual int marginHeight() const = 0;
   virtual bool allowFullscreen() const = 0;
+  virtual bool allowPaymentRequest() const = 0;
   virtual const WebVector<WebPermissionType>& delegatedPermissions() const = 0;
 };
 
@@ -64,6 +65,7 @@ class CORE_EXPORT DummyFrameOwner
   int marginWidth() const override { return -1; }
   int marginHeight() const override { return -1; }
   bool allowFullscreen() const override { return false; }
+  bool allowPaymentRequest() const override { return false; }
   const WebVector<WebPermissionType>& delegatedPermissions() const override {
     DEFINE_STATIC_LOCAL(WebVector<WebPermissionType>, permissions, ());
     return permissions;