Revert of Move base/prefs to components/prefs

base/prefs/pref_change_registrar.h

 // Copyright (c) 2010 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.
 
-// TODO(brettw) remove this forwarding header when prefs is completely moved to
-// components.
-#include "components/prefs/pref_change_registrar.h"
+#ifndef BASE_PREFS_PREF_CHANGE_REGISTRAR_H_
+#define BASE_PREFS_PREF_CHANGE_REGISTRAR_H_
+
+#include <map>
+#include <string>
+
+#include "base/callback.h"
+#include "base/macros.h"
+#include "base/prefs/base_prefs_export.h"
+#include "base/prefs/pref_observer.h"
+
+class PrefService;
+
+// Automatically manages the registration of one or more pref change observers
+// with a PrefStore. Functions much like NotificationRegistrar, but specifically
+// manages observers of preference changes. When the Registrar is destroyed,
+// all registered observers are automatically unregistered with the PrefStore.
+class BASE_PREFS_EXPORT PrefChangeRegistrar : public PrefObserver {
+ public:
+  // You can register this type of callback if you need to know the
+  // path of the preference that is changing.
+  typedef base::Callback<void(const std::string&)> NamedChangeCallback;
+
+  PrefChangeRegistrar();
+  virtual ~PrefChangeRegistrar();
+
+  // Must be called before adding or removing observers. Can be called more
+  // than once as long as the value of |service| doesn't change.
+  void Init(PrefService* service);
+
+  // Adds a pref observer for the specified pref |path| and |obs| observer
+  // object. All registered observers will be automatically unregistered
+  // when the registrar's destructor is called.
+  //
+  // The second version binds a callback that will receive the path of
+  // the preference that is changing as its parameter.
+  //
+  // Only one observer may be registered per path.
+  void Add(const std::string& path, const base::Closure& obs);
+  void Add(const std::string& path, const NamedChangeCallback& obs);
+
+  // Removes the pref observer registered for |path|.
+  void Remove(const std::string& path);
+
+  // Removes all observers that have been previously added with a call to Add.
+  void RemoveAll();
+
+  // Returns true if no pref observers are registered.
+  bool IsEmpty() const;
+
+  // Check whether |pref| is in the set of preferences being observed.
+  bool IsObserved(const std::string& pref);
+
+  // Check whether any of the observed preferences has the managed bit set.
+  bool IsManaged();
+
+  // Return the PrefService for this registrar.
+  PrefService* prefs();
+  const PrefService* prefs() const;
+
+ private:
+  // PrefObserver:
+  void OnPreferenceChanged(PrefService* service,
+                           const std::string& pref_name) override;
+
+  static void InvokeUnnamedCallback(const base::Closure& callback,
+                                    const std::string& pref_name);
+
+  typedef std::map<std::string, NamedChangeCallback> ObserverMap;
+
+  ObserverMap observers_;
+  PrefService* service_;
+
+  DISALLOW_COPY_AND_ASSIGN(PrefChangeRegistrar);
+};
+
+#endif  // BASE_PREFS_PREF_CHANGE_REGISTRAR_H_