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

ios/chrome/browser/file_metadata_util.mm

 // 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.
 
 #include "ios/chrome/browser/file_metadata_util.h"
 
 #import <Foundation/Foundation.h>
 
 #include "base/logging.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/threading/thread_restrictions.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 void SetSkipSystemBackupAttributeToItem(const base::FilePath& path,
                                         bool skip_system_backup) {
   base::ThreadRestrictions::AssertIOAllowed();
 
   NSURL* file_url =
       [NSURL fileURLWithPath:base::SysUTF8ToNSString(path.value())];
   DCHECK([[NSFileManager defaultManager] fileExistsAtPath:file_url.path]);
 
   NSError* error = nil;
   BOOL success = [file_url setResourceValue:(skip_system_backup ? @YES : @NO)
                                      forKey:NSURLIsExcludedFromBackupKey
                                       error:&error];
   if (!success) {
     LOG(ERROR) << [[error description] UTF8String];
   }
 }