Gate web payments iframe support on runtime enabled feature.

third_party/WebKit/Source/modules/payments/PaymentRequest.cpp

Index: third_party/WebKit/Source/modules/payments/PaymentRequest.cpp
diff --git a/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp b/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp
index 95a48b3223cf17c088e4c0ed8ad0fcabe7e3d13e..3170f08b9a4c710cd7331c9c7f23f22db4d89739 100644
--- a/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp
+++ b/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp
@@ -482,8 +482,10 @@ bool allowedToUsePaymentRequest(const Frame* frame) {
   // is an iframe element with an |allowpaymentrequest| attribute specified, and
   // whose node document is allowed to use the feature indicated by
   // |allowpaymentrequest|, then return true.
-  if (frame->owner() && frame->owner()->allowPaymentRequest())
+  if (RuntimeEnabledFeatures::paymentRequestIFrameEnabled() && frame->owner() &&
+      frame->owner()->allowPaymentRequest()) {
     return allowedToUsePaymentRequest(frame->tree().parent());
+  }
 
   // 4. Return false.
   return false;