Adding mediator for Sign-in promo

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

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 bundle_data("resources") {
   sources = [
     "resources/app_icon_placeholder.png",
     "resources/app_icon_placeholder@2x.png",
     "resources/app_icon_placeholder@3x.png",
     "resources/encryption_error.png",
@@ skipping 140 matching lines @@
     "//ios/chrome/browser/prefs",
     "//ios/chrome/browser/search_engines",
     "//ios/chrome/browser/signin",
     "//ios/chrome/browser/store_kit",
     "//ios/chrome/browser/sync",
     "//ios/chrome/browser/translate",
     "//ios/chrome/browser/ui",
     "//ios/chrome/browser/ui/alert_coordinator",
     "//ios/chrome/browser/ui/authentication",
     "//ios/chrome/browser/ui/authentication:authentication_arc",
+    "//ios/chrome/browser/ui/authentication:authentication_ui",
     "//ios/chrome/browser/ui/autofill/cells",
     "//ios/chrome/browser/ui/collection_view",
     "//ios/chrome/browser/ui/colors",
     "//ios/chrome/browser/ui/commands",
     "//ios/chrome/browser/ui/content_suggestions",
     "//ios/chrome/browser/ui/contextual_search",
     "//ios/chrome/browser/ui/icons",
     "//ios/chrome/browser/ui/keyboard",
     "//ios/chrome/browser/ui/material_components",
     "//ios/chrome/browser/ui/settings/cells",
@@ skipping 199 matching lines @@
     "//ios/web:test_support",
     "//net",
     "//ui/base",
     "//url",
   ]
   libs = [
     "UIKit.framework",
     "XCTest.framework",
   ]
 }