Componentize PrefSyncableService and support classes.

chrome/browser/prefs/synced_pref_change_registrar.h

-// Copyright 2013 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 CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
-#define CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_
-
-#include <map>
-#include <string>
-
-#include "base/callback.h"
-#include "chrome/browser/prefs/pref_service_syncable.h"
-#include "chrome/browser/prefs/synced_pref_observer.h"
-
-// Manages the registration of one or more SyncedPrefObservers on a
-// PrefServiceSyncable. This is modeled after base::PrefChangeRegistrar, and
-// it should be used whenever it's necessary to determine whether a pref change
-// has come from sync or from some other mechanism (managed, UI, external, etc.)
-class SyncedPrefChangeRegistrar : public SyncedPrefObserver {
- public:
-  // Registered callbacks may optionally take a path argument.
-  // The boolean argument indicates whether (true) or not (false)
-  // the change was a result of syncing.
-  typedef base::Callback<void(bool)> ChangeCallback;
-  typedef base::Callback<void(const std::string&, bool)> NamedChangeCallback;
-
-  explicit SyncedPrefChangeRegistrar(PrefServiceSyncable* pref_service);
-  virtual ~SyncedPrefChangeRegistrar();
-
-  // Register an observer callback for sync change events on the pref at
-  // |path|. Only one callback may be registered per pref.
-  void Add(const char* path, const ChangeCallback& callback);
-  void Add(const char* path, const NamedChangeCallback& callback);
-
-  // Remove the registered observer for |path|.
-  void Remove(const char* path);
-
-  // Remove all registered observers.
-  void RemoveAll();
-
-  // Indicates whether or not an observer is already registered for |path|.
-  bool IsObserved(const char* path) const;
-
- private:
-  // SyncedPrefObserver implementation
-  void OnSyncedPrefChanged(const std::string& path, bool from_sync) override;
-
-  typedef std::map<std::string, NamedChangeCallback> ObserverMap;
-
-  PrefServiceSyncable* pref_service_;
-  ObserverMap observers_;
-
-  DISALLOW_COPY_AND_ASSIGN(SyncedPrefChangeRegistrar);
-};
-
-#endif  // CHROME_BROWSER_PREFS_SYNCED_PREF_CHANGE_REGISTRAR_H_