[Payments] Handle clicking back on the CVC unmask dialog

components/payments/core/autofill_payment_instrument.cc

Index: components/payments/core/autofill_payment_instrument.cc
diff --git a/components/payments/core/autofill_payment_instrument.cc b/components/payments/core/autofill_payment_instrument.cc
index e74b3892c589d144edd00bd205dbdfd57c92e12c..83ceebca9fe3d0b8a38d347f60d22a83e3fef3f8 100644
--- a/components/payments/core/autofill_payment_instrument.cc
+++ b/components/payments/core/autofill_payment_instrument.cc
@@ -113,7 +113,9 @@ void AutofillPaymentInstrument::OnFullCardRequestSucceeded(
 }
 
 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;
 }