[Web Payments] Add a mechanism to build item lists in the PR dialog.

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

Index: chrome/browser/ui/views/payments/payment_request_sheet_controller.cc
diff --git a/chrome/browser/ui/views/payments/payment_request_sheet_controller.cc b/chrome/browser/ui/views/payments/payment_request_sheet_controller.cc
index dacbde528177e8f6386b8d62f701d698d7a4940d..e25b0e33feb243cf37e1651f79425c4f27708b70 100644
--- a/chrome/browser/ui/views/payments/payment_request_sheet_controller.cc
+++ b/chrome/browser/ui/views/payments/payment_request_sheet_controller.cc
@@ -28,6 +28,10 @@ PaymentRequestSheetController::CreatePrimaryButton() {
   return nullptr;
 }
 
+std::unique_ptr<views::View> PaymentRequestSheetController::CreateExtraView() {
+  return nullptr;
+}
+
 void PaymentRequestSheetController::ButtonPressed(
     views::Button* sender, const ui::Event& event) {
   switch (static_cast<PaymentRequestCommonTags>(sender->tag())) {
@@ -92,23 +96,20 @@ std::unique_ptr<views::View> PaymentRequestSheetController::CreateFooterView() {
                      0, views::GridLayout::USE_PREF, 0, 0);
 
   layout->StartRow(0, 0);
-  std::unique_ptr<views::View> leading_buttons_container =
-      base::MakeUnique<views::View>();
-
-  // TODO(anthonyvd): Add the other buttons that can eventually go into this
-  // footer.
-
-  layout->AddView(leading_buttons_container.release());
+  std::unique_ptr<views::View> extra_view = CreateExtraView();
+  if (extra_view)
+    layout->AddView(extra_view.release());
+  else
+    layout->SkipColumns(1);
 
   std::unique_ptr<views::View> trailing_buttons_container =
       base::MakeUnique<views::View>();
 
-  constexpr int kButtonSpacing = 10;
   trailing_buttons_container->SetLayoutManager(new views::BoxLayout(
       views::BoxLayout::kHorizontal,
       kPaymentRequestRowHorizontalInsets,
       kPaymentRequestRowVerticalInsets,
-      kButtonSpacing));
+      kPaymentRequestButtonSpacing));
 
   std::unique_ptr<views::Button> primary_button = CreatePrimaryButton();
   if (primary_button)