Reland: Add support for $i18n{} localized strings to ios/web.

ios/chrome/browser/ui/webui/flags_ui.cc

Index: ios/chrome/browser/ui/webui/flags_ui.cc
diff --git a/ios/chrome/browser/ui/webui/flags_ui.cc b/ios/chrome/browser/ui/webui/flags_ui.cc
index 67968c2c68992e1a6c7cbeb23acfc9f93af2b071..76228168d7b85183248359ac40366fbb8d92e5b5 100644
--- a/ios/chrome/browser/ui/webui/flags_ui.cc
+++ b/ios/chrome/browser/ui/webui/flags_ui.cc
@@ -55,6 +55,10 @@ web::WebUIIOSDataSource* CreateFlagsUIHTMLSource(
   source->AddLocalizedString(flags_ui::kFlagsWarningHeader,
                              IDS_FLAGS_UI_WARNING_HEADER);
   source->AddLocalizedString(flags_ui::kFlagsBlurb, IDS_FLAGS_UI_WARNING_TEXT);
+  source->AddLocalizedString(flags_ui::kChannelPromoBeta,
+                             IDS_FLAGS_UI_PROMOTE_BETA_CHANNEL);
+  source->AddLocalizedString(flags_ui::kChannelPromoDev,
+                             IDS_FLAGS_UI_PROMOTE_DEV_CHANNEL);
   source->AddLocalizedString(flags_ui::kFlagsUnsupportedTableTitle,
                              IDS_FLAGS_UI_UNSUPPORTED_TABLE_TITLE);
   source->AddLocalizedString(flags_ui::kFlagsNotSupported,