Upstream Chrome on iOS source code [8/11].

ios/chrome/browser/ui/settings/utils/observable_boolean.h

+// 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.
+
+#ifndef IOS_CHROME_BROWSER_UI_SETTINGS_UTILS_OBSERVABLE_BOOLEAN_H_
+#define IOS_CHROME_BROWSER_UI_SETTINGS_UTILS_OBSERVABLE_BOOLEAN_H_
+
+#import <Foundation/Foundation.h>
+
+@protocol BooleanObserver;
+
+// Describes the trait an observable boolean has.
+@protocol ObservableBoolean<NSObject>
+
+// The value of this observable boolean.
+@property(nonatomic, assign) BOOL value;
+
+// The observer subscribing to this observable boolean's changes notifications.
+@property(nonatomic, assign) id<BooleanObserver> observer;
+
+@end
+
+// Observer protocol for boolean changes.
+@protocol BooleanObserver
+
+// Called when the boolean changes. Note that all classes conforming to this
+// protocol might send this callback even when the value is reset to the same
+// value. This is the case for ContentSettingBackedBoolean for example.
+- (void)booleanDidChange:(id<ObservableBoolean>)observableBoolean;
+
+@end
+
+#endif  // IOS_CHROME_BROWSER_UI_SETTINGS_UTILS_OBSERVABLE_BOOLEAN_H_