Adding mediator for Sign-in promo

ios/chrome/browser/ui/authentication/BUILD.gn

Index: ios/chrome/browser/ui/authentication/BUILD.gn
diff --git a/ios/chrome/browser/ui/authentication/BUILD.gn b/ios/chrome/browser/ui/authentication/BUILD.gn
index b41e78c1e9871413bf087673b62c20dc1fb3f29f..2550592c91ddc04c384f37ae0fa6551a2e78b9f7 100644
--- a/ios/chrome/browser/ui/authentication/BUILD.gn
+++ b/ios/chrome/browser/ui/authentication/BUILD.gn
@@ -87,13 +87,22 @@ source_set("authentication_arc") {
     "account_control_item.mm",
     "resized_avatar_cache.h",
     "resized_avatar_cache.mm",
+    "signin_promo_item.h",
+    "signin_promo_item.mm",
+    "signin_promo_view.h",
+    "signin_promo_view.mm",
+    "signin_promo_view_mediator.h",
+    "signin_promo_view_mediator.mm",
   ]
   deps = [
+    "//base",
+    "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/collection_view/cells",
     "//ios/chrome/browser/ui/colors",
     "//ios/public/provider/chrome/browser",
     "//ios/public/provider/chrome/browser/signin",
+    "//ui/base",
   ]
   libs = [
     "CoreGraphics.framework",
@@ -110,6 +119,8 @@ source_set("unit_tests") {
     "authentication_flow_unittest.mm",
     "re_signin_infobar_delegate_unittest.mm",
     "signed_in_accounts_view_controller_unittest.mm",
+    "signin_promo_item_unittest.mm",
+    "signin_promo_view_mediator_unittest.mm",
   ]
   deps = [
     ":authentication",