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

ios/chrome/browser/ui/settings/utils/pref_backed_boolean.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.
 
 #import "ios/chrome/browser/ui/settings/utils/pref_backed_boolean.h"
 
 #include "base/bind.h"
 #include "components/prefs/pref_member.h"
 #include "components/prefs/pref_service.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Adaptor function to allow invoking onChange as a base::Closure.
 void OnChange(id<ObservableBoolean> object) {
   [object.observer booleanDidChange:object];
 }
 
 }  // namespace
 
 @implementation PrefBackedBoolean {
@@ skipping 19 matching lines @@
 
 - (BOOL)value {
   return _pref.GetValue();
 }
 
 - (void)setValue:(BOOL)value {
   _pref.SetValue(value == YES);
 }
 
 @end