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

ios/chrome/browser/ui/settings/utils/fake_observable_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/fake_observable_boolean.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 @implementation FakeObservableBoolean
 
 @synthesize value = _value;
 @synthesize observer = _observer;
 
 - (void)setValue:(BOOL)value {
   bool changed = value != _value;
   _value = value;
   if (changed)
     [self.observer booleanDidChange:self];
 }
 
 @end
 
 @implementation TestBooleanObserver
 
 @synthesize updateCount = _updateCount;
 
 - (void)booleanDidChange:(id<ObservableBoolean>)observableBoolean {
   self.updateCount++;
 }
 
 @end