iframes with allowpaymentrequest attribute are allowed to make payment requests.

third_party/WebKit/Source/modules/modules_idl_files.gni

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//third_party/WebKit/Source/bindings/bindings.gni")
 
 # The paths in this file are absolute since this file is imported and the
 # file lists must be valid from multple "current directories".
 
 bindings_modules_output_dir = "$bindings_output_dir/modules"
@@ skipping 553 matching lines @@
           "mediastream/NavigatorUserMedia.idl",
           "mediastream/URLMediaStream.idl",
           "mediastream/WindowMediaStream.idl",
           "navigatorcontentutils/NavigatorContentUtils.idl",
           "nfc/NavigatorNFC.idl",
           "netinfo/NavigatorNetworkInformation.idl",
           "netinfo/WorkerNavigatorNetworkInformation.idl",
           "notifications/ServiceWorkerGlobalScopeNotifications.idl",
           "notifications/ServiceWorkerRegistrationNotifications.idl",
           "offscreencanvas/OffscreenCanvasModules.idl",
+          "payments/HTMLIFrameElementPayments.idl",
           "permissions/NavigatorPermissions.idl",
           "permissions/WorkerNavigatorPermissions.idl",
           "plugins/NavigatorPlugins.idl",
           "presentation/NavigatorPresentation.idl",
           "push_messaging/ServiceWorkerGlobalScopePush.idl",
           "push_messaging/ServiceWorkerRegistrationPush.idl",
           "quota/NavigatorStorageQuota.idl",
           "quota/WindowQuota.idl",
           "quota/WorkerNavigatorStorageQuota.idl",
           "remoteplayback/HTMLMediaElementRemotePlayback.idl",
@@ skipping 303 matching lines @@
   "$blink_modules_output_dir/websockets/CloseEventInit.h",
   "$blink_modules_output_dir/webusb/USBConnectionEventInit.cpp",
   "$blink_modules_output_dir/webusb/USBConnectionEventInit.h",
   "$blink_modules_output_dir/webusb/USBControlTransferParameters.cpp",
   "$blink_modules_output_dir/webusb/USBControlTransferParameters.h",
   "$blink_modules_output_dir/webusb/USBDeviceFilter.cpp",
   "$blink_modules_output_dir/webusb/USBDeviceFilter.h",
   "$blink_modules_output_dir/webusb/USBDeviceRequestOptions.cpp",
   "$blink_modules_output_dir/webusb/USBDeviceRequestOptions.h",
 ]