[Payment Request] Refactors the remaining selector view controllers

ios/chrome/browser/payments/payment_request_selector_view_controller.h

Index: ios/chrome/browser/payments/payment_request_selector_view_controller.h
diff --git a/ios/chrome/browser/payments/payment_request_selector_view_controller.h b/ios/chrome/browser/payments/payment_request_selector_view_controller.h
index d9e1efe1a42c009cf5cb7e79ebb3888d94b27f31..7e9f56a184d38c9ce5f7f0d074a2af5ae533932e 100644
--- a/ios/chrome/browser/payments/payment_request_selector_view_controller.h
+++ b/ios/chrome/browser/payments/payment_request_selector_view_controller.h
@@ -20,15 +20,17 @@
             (PaymentRequestSelectorViewController*)controller
                         didSelectItemAtIndex:(NSUInteger)index;
 
-// Notifies the delegate that the user has chosen to add an item.
-- (void)paymentRequestSelectorViewControllerDidSelectAddItem:
-    (PaymentRequestSelectorViewController*)controller;
-
 // Notifies the delegate that the user has chosen to return to the previous
 // screen without making a selection.
 - (void)paymentRequestSelectorViewControllerDidFinish:
     (PaymentRequestSelectorViewController*)controller;
 
+@optional
+
+// Notifies the delegate that the user has chosen to add an item.
+- (void)paymentRequestSelectorViewControllerDidSelectAddItem:
+    (PaymentRequestSelectorViewController*)controller;
+
 @end
 
 // View controller responsible for presenting a list of items provided by the