Adding mediator for Sign-in promo

ios/chrome/browser/ui/authentication/signin_promo_item.h

+// Copyright 2017 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGNIN_PROMO_ITEM_H_
+#define IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGNIN_PROMO_ITEM_H_
+
+#import <UIKit/UIKit.h>
+
+#import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
+#import "ios/third_party/material_components_ios/src/components/CollectionCells/src/MaterialCollectionCells.h"
+
+@class SigninPromoView;
+@protocol SigninPromoViewConfigurator;
+
+// SigninPromoItem is an item that configures a SigninPromoCell cell.
+@interface SigninPromoItem : CollectionViewItem
+
+// Configures the SigninPromoView view from SigninPromoCell.
+@property(nonatomic, readonly, weak) id<SigninPromoViewConfigurator>
+    configurator;
+
+- (instancetype)initWithType:(NSInteger)type
+                configurator:(id<SigninPromoViewConfigurator>)configurator
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithType:(NSInteger)type NS_UNAVAILABLE;
+
+@end
+
+// Cell representation for SigninPromoItem. The cell contains only a
+// SigninPromoView view.
+@interface SigninPromoCell : MDCCollectionViewCell
+
+@property(nonatomic, strong) SigninPromoView* signinPromoView;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGNIN_PROMO_ITEM_H_