[Payments] Handle clicking back on the CVC unmask dialog

components/payments/core/autofill_payment_instrument.cc

 // Copyright 2017 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.
 
 #include "components/payments/core/autofill_payment_instrument.h"
 
 #include "base/json/json_writer.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "components/autofill/core/browser/autofill_country.h"
@@ skipping 95 matching lines @@
   DCHECK(delegate_);
   credit_card_ = card;
   cvc_ = cvc;
   is_waiting_for_card_unmask_ = false;
 
   if (!is_waiting_for_billing_address_normalization_)
     GenerateBasicCardResponse();
 }
 
 void AutofillPaymentInstrument::OnFullCardRequestFailed() {
-  // TODO(anthonyvd): Do something with the error.
+  // The user may have cancelled the unmask or something has gone wrong (e.g.,
+  // the network request failed). In all cases, reset the |delegate_| so another
+  // request can start.
   delegate_ = nullptr;
 }
 
 void AutofillPaymentInstrument::OnAddressNormalized(
     const autofill::AutofillProfile& normalized_profile) {
   DCHECK(is_waiting_for_billing_address_normalization_);
 
   billing_address_ = normalized_profile;
   is_waiting_for_billing_address_normalization_ = false;
 
@@ skipping 19 matching lines @@
           .ToDictionaryValue();
   std::string stringified_details;
   base::JSONWriter::Write(*response_value, &stringified_details);
   delegate_->OnInstrumentDetailsReady(method_name(), stringified_details);
 
   delegate_ = nullptr;
   cvc_ = base::UTF8ToUTF16("");
 }
 
 }  // namespace payments