Revert of Move base/prefs to components/prefs

base/prefs/scoped_user_pref_update.h

Index: base/prefs/scoped_user_pref_update.h
diff --git a/base/prefs/scoped_user_pref_update.h b/base/prefs/scoped_user_pref_update.h
index ce03c6a830da2e493eb8d80ed574832bae58914a..29ad8526cd3c3c91630cd58a71f631be136e371a 100644
--- a/base/prefs/scoped_user_pref_update.h
+++ b/base/prefs/scoped_user_pref_update.h
@@ -1,7 +1,108 @@
 // 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.
 
-// TODO(brettw) remove this forwarding header when prefs is completely moved to
-// components.
-#include "components/prefs/scoped_user_pref_update.h"
+#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_