[SecurePaymentConfirmation] Correct separator color

Set the separator color to the themed color rather than explicitly. This
also ensures the separator is displayed properly in dark mode.

Bug: 1110322
Change-Id: If5118967106eccdced837fcad8a45757a68d2315
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2368177Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Nick Burris <nburris@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800381}

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

@@ -323,8 +323,10 @@ std::unique_ptr<views::View> SecurePaymentConfirmationDialogView::CreateRowView(
     DialogViewID icon_id) {
   std::unique_ptr<views::View> row = std::make_unique<views::View>();
 
-  row->SetBorder(
-      views::CreateSolidSidedBorder(0, 0, 1, 0, gfx::kGoogleGrey200));
+  row->SetBorder(views::CreateSolidSidedBorder(
+      0, 0, 1, 0,
+      GetNativeTheme()->GetSystemColor(
+          ui::NativeTheme::kColorId_SeparatorColor)));
 
   views::GridLayout* layout =
       row->SetLayoutManager(std::make_unique<views::GridLayout>());