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

ios/chrome/browser/ui/ntp/most_visited_layout.mm

 // Copyright 2014 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.
 
 #import "ios/chrome/browser/ui/ntp/most_visited_layout.h"
 
 #import "ios/chrome/browser/ui/ntp/new_tab_page_header_constants.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation MostVisitedLayout
 
 - (NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {
-  NSMutableArray* layoutAttributes = [
-      [[super layoutAttributesForElementsInRect:rect] mutableCopy] autorelease];
+  NSMutableArray* layoutAttributes =
+      [[super layoutAttributesForElementsInRect:rect] mutableCopy];
   UICollectionViewLayoutAttributes* fixedHeaderAttributes = nil;
   NSIndexPath* fixedHeaderIndexPath =
       [NSIndexPath indexPathForItem:0 inSection:0];
 
   for (UICollectionViewLayoutAttributes* attributes in layoutAttributes) {
     if ([attributes.representedElementKind
             isEqualToString:UICollectionElementKindSectionHeader] &&
         attributes.indexPath.section == fixedHeaderIndexPath.section) {
       fixedHeaderAttributes = [self
           layoutAttributesForSupplementaryViewOfKind:
@@ skipping 69 matching lines @@
     minimumHeight -= ntp_header::kToolbarHeight;
 
   CGSize contentSize = [super collectionViewContentSize];
   if (contentSize.height < minimumHeight) {
     contentSize.height = minimumHeight;
   }
   return contentSize;
 }
 
 @end