[Web Payments] Implement the CVC Unmask dialog.

components/payments/content/payment_request.cc

Index: components/payments/content/payment_request.cc
diff --git a/components/payments/content/payment_request.cc b/components/payments/content/payment_request.cc
index ed48db057bf30588400e06c8a5f6d8b336445309..77b4449bdaa85601fa644288333b3d852b808965 100644
--- a/components/payments/content/payment_request.cc
+++ b/components/payments/content/payment_request.cc
@@ -4,6 +4,7 @@
 
 #include "components/payments/content/payment_request.h"
 
+#include <string>
 #include <utility>
 
 #include "base/memory/ptr_util.h"
@@ -105,6 +106,10 @@ void PaymentRequest::OnPaymentResponseAvailable(
   client_->OnPaymentResponse(std::move(response));
 }
 
+PaymentRequestDelegate* PaymentRequest::GetPaymentRequestDelegate() {
+  return delegate_.get();
+}
+
 void PaymentRequest::UserCancelled() {
   // If |client_| is not bound, then the object is already being destroyed as
   // a result of a renderer event.