[Payments] Handle clicking back on the CVC unmask dialog

Was previously crashing because the AutofillPaymentInstrument delegate
was not being reset properly on back navigation. Now it is.

BUG=715093
TEST=browser_tests

Review-Url: https://codereview.chromium.org/2844293002
Cr-Commit-Position: refs/heads/master@{#467747}

chrome/browser/ui/views/payments/cvc_unmask_view_controller.cc

@@ -109,7 +109,8 @@ void CvcUnmaskViewController::ShowUnmaskPrompt(
 
 void CvcUnmaskViewController::OnUnmaskVerificationResult(
     autofill::AutofillClient::PaymentsRpcResult result) {
-  // TODO(anthonyvd): Show result.
+  // TODO(crbug.com/716020): Handle FullCardRequest errors with more
+  // granularity and display an error in the UI.
 }
 
 base::string16 CvcUnmaskViewController::GetSheetTitle() {
@@ -183,6 +184,10 @@ void CvcUnmaskViewController::ButtonPressed(views::Button* sender,
     case static_cast<int>(Tags::CONFIRM_TAG):
       CvcConfirmed();
       break;
+    case static_cast<int>(PaymentRequestCommonTags::BACK_BUTTON_TAG):
+      unmask_delegate_->OnUnmaskPromptClosed();
+      dialog()->GoBack();
+      break;
     default:
       PaymentRequestSheetController::ButtonPressed(sender, event);
   }

chrome/browser/ui/views/payments/cvc_unmask_view_controller_browsertest.cc

@@ -8,17 +8,19 @@
 
 namespace payments {
 
-class CvcUnmaskViewControllerTest : public PaymentRequestBrowserTestBase {
+class PaymentRequestCvcUnmaskViewControllerTest
+    : public PaymentRequestBrowserTestBase {
  protected:
-  CvcUnmaskViewControllerTest()
+  PaymentRequestCvcUnmaskViewControllerTest()
       : PaymentRequestBrowserTestBase(
             "/payment_request_no_shipping_test.html") {}
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(CvcUnmaskViewControllerTest);
+  DISALLOW_COPY_AND_ASSIGN(PaymentRequestCvcUnmaskViewControllerTest);
 };
 
-IN_PROC_BROWSER_TEST_F(CvcUnmaskViewControllerTest, CvcSentToResponse) {
+IN_PROC_BROWSER_TEST_F(PaymentRequestCvcUnmaskViewControllerTest,
+                       CvcSentToResponse) {
   AddCreditCard(autofill::test::GetCreditCard());  // Visa.
 
   InvokePaymentRequestUI();
@@ -28,4 +30,21 @@ IN_PROC_BROWSER_TEST_F(CvcUnmaskViewControllerTest, CvcSentToResponse) {
   ExpectBodyContains({"\"cardSecurityCode\": \"012\""});
 }
 
+// Test that going in the CVC editor, backing out and opening it again to pay
+// does not crash.
+IN_PROC_BROWSER_TEST_F(PaymentRequestCvcUnmaskViewControllerTest,
+                       OpenGoBackOpenPay) {
+  AddCreditCard(autofill::test::GetCreditCard());  // Visa.
+
+  InvokePaymentRequestUI();
+  OpenCVCPromptWithCVC(base::ASCIIToUTF16("012"));
+
+  // Go back before confirming the CVC.
+  ClickOnBackArrow();
+
+  // Now pay for real.
+  PayWithCreditCardAndWait(base::ASCIIToUTF16("012"));
+  ExpectBodyContains({"\"cardSecurityCode\": \"012\""});
+}
+
 }  // namespace payments

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;
 }