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;
+

[lpromero, 2017/03/24 10:36:19]

Remove empty line.

[jlebel, 2017/03/24 20:59:08]

Done.

+@protocol SigninPromoViewConfigurator;
+
+// SigninPromoItem is an item that configures a SigninPromoCell cell.
+@interface SigninPromoItem : CollectionViewItem
+
+// Configures the SigninPromoView view from SigninPromoCell.
+@property(nonatomic, weak) id<SigninPromoViewConfigurator>
+    signinPromoViewConfigurator;

[msarda, 2017/03/22 12:18:38]

Optional nit: s/signinPromoViewConfigurator/configurator

[lpromero, 2017/03/24 10:36:19]

+1

[jlebel, 2017/03/24 20:59:08]

Done.

+
+- (instancetype)initWithType:(NSInteger)type
+    signinPromoViewConfigurator:

[msarda, 2017/03/22 12:18:38]

Nit: s/signinPromoViewConfigurator/configurator for better code alignment.

[lpromero, 2017/03/24 10:36:19]

I would even just get rid of this initializer. People can initialize the item
then set the configurator?

Otherwise, please make the configurator readonly.

[jlebel, 2017/03/24 20:59:08]

Done.

+        (id<SigninPromoViewConfigurator>)signinPromoViewConfigurator
+    NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithType:(NSInteger)type NS_UNAVAILABLE;
+
+@end
+
+// Cell representation for SigninPromoItem. The cell contains only a

[msarda, 2017/03/22 12:18:38]

s/. The cell contains ../, containing a single SigninPromoView

[lpromero, 2017/03/24 10:36:19]

Disagreeing. The current comment is "more clearer", as we saw in the Tech
Writing 101 training :)

[jlebel, 2017/03/24 20:59:08]

Acknowledged.

+// SigninPromoView view.
+@interface SigninPromoCell : MDCCollectionViewCell
+
+@property(nonatomic, strong) SigninPromoView* signinPromoView;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGNIN_PROMO_ITEM_H_