Adding accessibility to the close button in sign-in promo

ios/chrome/browser/ui/authentication/signin_promo_view.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_SIGN_PROMO_VIEW_H_
 #define IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGN_PROMO_VIEW_H_
 
 #import <UIKit/UIKit.h>
 
 #include "components/signin/core/browser/signin_metrics.h"
@@ skipping 22 matching lines @@
 //   - the title for |primaryButton|
 //   - the title for |secondaryButton|
 @interface SigninPromoView : UIView
 
 @property(nonatomic, weak) id<SigninPromoViewDelegate> delegate;
 @property(nonatomic) SigninPromoViewMode mode;
 @property(nonatomic, readonly) UIImageView* imageView;
 @property(nonatomic, readonly) UILabel* textLabel;
 @property(nonatomic, readonly) MDCFlatButton* primaryButton;
 @property(nonatomic, readonly) MDCFlatButton* secondaryButton;
+// Hidden by default.
+@property(nonatomic, readonly) UIButton* closeButton;
 
 // Horizontal padding used for |textLabel|, |primaryButton| and
 // |secondaryButton|. Used to compute the preferred max layout width of
 // |textLabel|.
 @property(nonatomic, readonly) CGFloat horizontalPadding;
 
 - (instancetype)initWithCoder:(NSCoder*)aDecoder NS_UNAVAILABLE;
 
 // Sets the image in |imageView|. This method will add a circular background
 // using CircularImageFromImage() (so if the image is not squared, it will be
 // cropped first). Must only be called in the "Warm State" mode.
 - (void)setProfileImage:(UIImage*)image;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_AUTHENTICATION_SIGN_PROMO_VIEW_H_