Revert of Move base/prefs to components/prefs

components/prefs/scoped_user_pref_update.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.
-//
-// A helper class that assists preferences in firing notifications when lists
-// or dictionaries are changed.
-
-#ifndef BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
-#define BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_
-
-#include <string>
-
-#include "base/macros.h"
-#include "base/prefs/base_prefs_export.h"
-#include "base/prefs/pref_service.h"
-#include "base/threading/non_thread_safe.h"
-#include "base/values.h"
-
-class PrefService;
-
-namespace base {
-class DictionaryValue;
-class ListValue;
-}
-
-namespace subtle {
-
-// Base class for ScopedUserPrefUpdateTemplate that contains the parts
-// that do not depend on ScopedUserPrefUpdateTemplate's template parameter.
-//
-// We need this base class mostly for making it a friend of PrefService
-// and getting access to PrefService::GetMutableUserPref and
-// PrefService::ReportUserPrefChanged.
-class BASE_PREFS_EXPORT ScopedUserPrefUpdateBase : public base::NonThreadSafe {
- protected:
-  ScopedUserPrefUpdateBase(PrefService* service, const std::string& path);
-
-  // Calls Notify().
-  ~ScopedUserPrefUpdateBase();
-
-  // Sets |value_| to |service_|->GetMutableUserPref and returns it.
-  base::Value* GetValueOfType(base::Value::Type type);
-
- private:
-  // If |value_| is not null, triggers a notification of PrefObservers and
-  // resets |value_|.
-  void Notify();
-
-  // Weak pointer.
-  PrefService* service_;
-  // Path of the preference being updated.
-  std::string path_;
-  // Cache of value from user pref store (set between Get() and Notify() calls).
-  base::Value* value_;
-
-  DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdateBase);
-};
-
-}  // namespace subtle
-
-// Class to support modifications to DictionaryValues and ListValues while
-// guaranteeing that PrefObservers are notified of changed values.
-//
-// This class may only be used on the UI thread as it requires access to the
-// PrefService.
-template <typename T, base::Value::Type type_enum_value>
-class ScopedUserPrefUpdate : public subtle::ScopedUserPrefUpdateBase {
- public:
-  ScopedUserPrefUpdate(PrefService* service, const std::string& path)
-      : ScopedUserPrefUpdateBase(service, path) {}
-
-  // Triggers an update notification if Get() was called.
-  virtual ~ScopedUserPrefUpdate() {}
-
-  // Returns a mutable |T| instance that
-  // - is already in the user pref store, or
-  // - is (silently) created and written to the user pref store if none existed
-  //   before.
-  //
-  // Calling Get() implies that an update notification is necessary at
-  // destruction time.
-  //
-  // The ownership of the return value remains with the user pref store.
-  // Virtual so it can be overriden in subclasses that transform the value
-  // before returning it (for example to return a subelement of a dictionary).
-  virtual T* Get() {
-    return static_cast<T*>(GetValueOfType(type_enum_value));
-  }
-
-  T& operator*() {
-    return *Get();
-  }
-
-  T* operator->() {
-    return Get();
-  }
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ScopedUserPrefUpdate);
-};
-
-typedef ScopedUserPrefUpdate<base::DictionaryValue,
-                             base::Value::TYPE_DICTIONARY>
-    DictionaryPrefUpdate;
-typedef ScopedUserPrefUpdate<base::ListValue, base::Value::TYPE_LIST>
-    ListPrefUpdate;
-
-#endif  // BASE_PREFS_SCOPED_USER_PREF_UPDATE_H_