[ObjC ARC] Converts ios/chrome/browser/ui/ntp:ntp_internal to ARC.

ios/chrome/browser/ui/ntp/whats_new_header_view.h

 // Copyright 2015 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_NTP_WHATS_NEW_HEADER_VIEW_H_
 #define IOS_CHROME_BROWSER_UI_NTP_WHATS_NEW_HEADER_VIEW_H_
 
 #import <UIKit/UIKit.h>
 
 #import "ios/chrome/browser/ui/ntp/notification_promo_whats_new.h"
 #include "ios/public/provider/chrome/browser/images/whats_new_icon.h"
 
 @protocol WhatsNewHeaderViewDelegate<NSObject>
 
 - (void)onPromoLabelTapped;
 
 @end
 
 @interface WhatsNewHeaderView : UICollectionReusableView
 
-@property(nonatomic, assign) id<WhatsNewHeaderViewDelegate> delegate;
+@property(nonatomic, weak) id<WhatsNewHeaderViewDelegate> delegate;
 
 // Sets the text for the attributed label.
 - (void)setText:(NSString*)text;
 
 // Sets the icon of the view.
 - (void)setIcon:(WhatsNewIcon)icon;
 
 // Sets the value to use for the left and right margin.
 - (void)setSideMargin:(CGFloat)sideMargin forWidth:(CGFloat)width;
 
 // Returns the minimum height required for WhatsNewHeaderView to fit in |width|,
 // for a given |text|.
 + (int)heightToFitText:(NSString*)text inWidth:(CGFloat)width;
 
 @end
 
 #endif  // IOS_CHROME_BROWSER_UI_NTP_WHATS_NEW_HEADER_VIEW_H_