[iOS] Upstream observer bridges

ios/chrome/browser/prefs/pref_observer_bridge.h

+// Copyright 2012 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_PREFS_PREF_OBSERVER_BRIDGE_H_
+#define IOS_CHROME_BROWSER_PREFS_PREF_OBSERVER_BRIDGE_H_
+
+#include <string>
+
+#include "base/compiler_specific.h"
+
+class PrefChangeRegistrar;
+
+@protocol PrefObserverDelegate
+- (void)onPreferenceChanged:(const std::string&)preferenceName;
+@end
+
+class PrefObserverBridge {
+ public:
+  explicit PrefObserverBridge(id<PrefObserverDelegate> delegate);
+  virtual ~PrefObserverBridge();
+
+  virtual void ObserveChangesForPreference(const std::string& pref_name,
+                                           PrefChangeRegistrar* registrar);
+
+ private:
+  virtual void OnPreferenceChanged(const std::string& pref_name);
+
+  id<PrefObserverDelegate> delegate_;
+};
+
+#endif  // IOS_CHROME_BROWSER_PREFS_PREF_OBSERVER_BRIDGE_H_