Add ManagedUserSettingsService and a SupervisedUserPrefStore using it.

chrome/browser/managed_mode/managed_user_settings_service.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_MANAGED_MODE_MANAGED_USER_SETTINGS_SERVICE_H_
+#define CHROME_BROWSER_MANAGED_MODE_MANAGED_USER_SETTINGS_SERVICE_H_
+
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/values.h"
+#include "chrome/browser/managed_mode/managed_users.h"
+
+// Defines an abstract base class for a service that stores managed user

[Pam (message me for reviews), 2013/09/03 10:45:32]

It doesn't just store the settings -- that would be more the job of the
PrefStore. Its main purpose is to keep track of the meta-state of the settings
and inform the PrefStore. Or something like that.

[Bernhard Bauer, 2013/09/03 10:53:43]

Well, it does store the settings in the sense that it is the authoritative
source of managed user settings. The PrefStore really just translates them from
internal keys to preferences.
Mmm, meta-state... :)

But yeah, this is going away anyway.

+// settings, which are key-value pairs configured by a different user to
+// control certain browser behaviors for managed users.
+// Setting names are defined in managed_user_constants.h.
+class ManagedUserSettingsService {
+ public:
+  // A callback whose first parameter is a dictionary containing all managed
+  // user settings. If the dictionary is NULL, it means that the service is
+  // inactive, i.e. the user is not managed.
+  typedef base::Callback<void(const base::DictionaryValue*)> SettingsCallback;
+
+  // Adds a callback to be called when managed user settings are initially
+  // available, or when they change.
+  void Subscribe(const SettingsCallback& callback);
+
+  // Activates the service. This happens when the user is managed.
+  void Activate();
+
+ protected:
+  ManagedUserSettingsService();
+  virtual ~ManagedUserSettingsService();
+
+  // Sends the settings to all subscribers. This method should be called by the
+  // subclass whenever the settings change.
+  void InformSubscribers();
+
+ private:
+  // Whether managed user settings are available.
+  virtual bool IsReady() const = 0;
+
+  // Returns a dictionary with all managed user settings. This method will
+  // only be called once IsReady() returns true.
+  virtual scoped_ptr<base::DictionaryValue> GetSettings() const = 0;
+
+  // Returns the dictionary produced by GetSettings() above if the service is
+  // active, or NULL otherwise.
+  scoped_ptr<base::DictionaryValue> GetSettingsIfActive();
+
+  bool active_;
+
+  std::vector<SettingsCallback> subscribers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ManagedUserSettingsService);
+};
+
+#endif  // CHROME_BROWSER_MANAGED_MODE_MANAGED_USER_SETTINGS_SERVICE_H_