[ObjC ARC] Converts ios/chrome/app/startup:startup to ARC.

ios/chrome/app/startup/register_experimental_settings.mm

 // Copyright 2016 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/app/startup/register_experimental_settings.h"
 
 #include "base/logging.h"
 #include "base/mac/bundle_locations.h"
-#import "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Key in the UserDefaults for the Experimental Keys.
 NSString* kExperimentalKeysKey = @"ExperimentalKeys";
 
 // Returns YES if a setting value is equivalent to not having the setting at
 // all. This must always be true for default values, otherwise the experimental
 // settings will have different default behaviors in stable channel (where the
 // bundle isn't present).
 BOOL IsDefaultSettingValueValid(id value) {
   if (!value)
@@ skipping 25 matching lines @@
   NSDictionary* infoDictionary = [bundle infoDictionary];
   NSString* version = [infoDictionary objectForKey:@"CFBundleVersion"];
   [userDefaults setObject:version forKey:@"Version"];
 
   NSString* bundlePath = [bundle bundlePath];
   NSString* settingsFilepath =
       [bundlePath stringByAppendingPathComponent:@"Settings.bundle"];
   NSArray* settingsContent =
       [[NSFileManager defaultManager] contentsOfDirectoryAtPath:settingsFilepath
                                                           error:NULL];
-  base::scoped_nsobject<NSMutableArray> currentExpKeys(
-      [[NSMutableArray alloc] init]);
+  NSMutableArray* currentExpKeys = [[NSMutableArray alloc] init];
 
   for (NSString* filename in settingsContent) {
     // Only plist files are preferences definition.
     if ([[filename pathExtension] isEqualToString:@"plist"]) {
       NSString* filepath =
           [settingsFilepath stringByAppendingPathComponent:filename];
       NSArray* registeredKeys =
           [self registerExperimentalSettingsForFile:filepath
                                        userDefaults:userDefaults];
       [currentExpKeys addObjectsFromArray:registeredKeys];
@@ skipping 50 matching lines @@
     id currentValue = [userDefaults objectForKey:keyValue];
     if (currentValue &&
         (!defaultValue || [currentValue isEqual:defaultValue])) {
       [userDefaults removeObjectForKey:keyValue];
     }
   }
   return registeredKeys;
 }
 
 @end