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

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

 // Copyright 2012 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/centering_scrollview.h"
 
 #include "base/logging.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Thickness of scrollbar images inserted by UIScrollView (circa iOS 5.0).
 const CGFloat kScrollBarThickness = 7.0;
 }  // namespace
 
 @interface CenteringScrollView ()
 // Returns the one and only subview. There may be other subviews
 // (e.g. UIImageView for the scrollbars) created by UIScrollView.
 - (UIView*)findContentView;
 @end
@@ skipping 47 matching lines @@
         thickness <= kScrollBarThickness)
       continue;
     soloView = view;
     ++viewCount;
   }
   DCHECK(viewCount == 1);
   return soloView;
 }
 
 @end