[Payments] Add an entry for Payment Request to chrome://flags on iOS

ios/chrome/browser/ui/browser_view_controller.mm

Index: ios/chrome/browser/ui/browser_view_controller.mm
diff --git a/ios/chrome/browser/ui/browser_view_controller.mm b/ios/chrome/browser/ui/browser_view_controller.mm
index 39998f932e028135ac6d658fe41d91f3b28f5318..19c57b229f0809f308818db71a624a637cf9cbdd 100644
--- a/ios/chrome/browser/ui/browser_view_controller.mm
+++ b/ios/chrome/browser/ui/browser_view_controller.mm
@@ -16,6 +16,7 @@
 
 #include "base/base64.h"
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/format_macros.h"
 #include "base/i18n/rtl.h"
@@ -37,6 +38,7 @@
 #include "components/bookmarks/browser/bookmark_model.h"
 #include "components/image_fetcher/ios/ios_image_data_fetcher_wrapper.h"
 #include "components/infobars/core/infobar_manager.h"
+#include "components/payments/core/features.h"
 #include "components/prefs/pref_service.h"
 #include "components/reading_list/core/reading_list_model.h"
 #include "components/search_engines/search_engines_pref_names.h"
@@ -1835,7 +1837,7 @@ class BrowserBookmarkModelBridge : public bookmarks::BookmarkModelObserver {
     [_contextualSearchController setTab:[_model currentTab]];
   }
 
-  if (experimental_flags::IsPaymentRequestEnabled()) {
+  if (base::FeatureList::IsEnabled(payments::features::kWebPayments)) {
     _paymentRequestManager = [[PaymentRequestManager alloc]
         initWithBaseViewController:self
                       browserState:_browserState];