[Web Payments] Add PopMany and Size functions to ViewStack

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

Index: chrome/browser/ui/views/payments/payment_request_dialog_view.cc
diff --git a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
index eb88d2fea5b15b3b9ac5993e2952269ded2173d1..a43851a04120571ab6d3a6fb7f2f67e56f79a631 100644
--- a/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
+++ b/chrome/browser/ui/views/payments/payment_request_dialog_view.cc
@@ -152,6 +152,16 @@ void PaymentRequestDialogView::GoBack() {
     observer_for_testing_->OnBackNavigation();
 }
 
+void PaymentRequestDialogView::GoBackToPaymentSheet() {
+  // This assumes that the Payment Sheet is the first view in the stack. Thus if
+  // there is only one view, we are already showing the payment sheet.
+  if (view_stack_->size() > 1)
+    view_stack_->PopMany(view_stack_->size() - 1);
+
+  if (observer_for_testing_)
+    observer_for_testing_->OnBackToPaymentSheetNavigation();
+}
+
 void PaymentRequestDialogView::ShowContactProfileSheet() {
   view_stack_->Push(
       CreateViewAndInstallController(