Add policy for limiting the session length

chrome/browser/chromeos/session_length_limiter.h

+// Copyright (c) 2012 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_CHROMEOS_SESSION_LENGTH_LIMITER_H_
+#define CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/observer_list.h"
+#include "base/prefs/public/pref_change_registrar.h"
+#include "base/threading/thread_checker.h"
+#include "base/time.h"
+#include "base/timer.h"
+#include "chrome/browser/profiles/profile_keyed_service.h"
+
+class PrefService;
+
+namespace chromeos {
+
+class SessionLengthLimiter : public ProfileKeyedService {
+ public:
+  class Observer {
+   public:
+    // Notification of the remaining session time, sent by the
+    // SessionLengthLimiter once per second. When there is no limit or the limit
+    // is removed, the notification is invoked one more time with |remaining|
+    // set to |NULL|.
+    virtual void SessionTimeRemainingChanged(
+        const base::TimeDelta* remaining) = 0;
+
+   protected:
+    virtual ~Observer();
+  };
+
+  class Delegate {
+   public:
+    virtual ~Delegate();
+
+    virtual const base::Time GetCurrentTime() const = 0;
+    virtual void Logout() = 0;

[Mattias Nissler (ping if slow), 2012/12/12 10:12:57]

Call this StopSession() maybe?

[bartfab (slow), 2012/12/13 16:22:48]

Done.

+  };
+
+  SessionLengthLimiter(Delegate* delegate, PrefService* prefs);
+  virtual ~SessionLengthLimiter();
+
+  // ProfileKeyedService:
+  virtual void Shutdown() OVERRIDE;
+
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+ private:
+  base::ThreadChecker thread_checker_;
+
+  scoped_ptr<Delegate> delegate_;
+  PrefChangeRegistrar pref_change_registrar_;

[Mattias Nissler (ping if slow), 2012/12/12 10:12:57]

Might want to use an IntegerPrefMember instead.

[bartfab (slow), 2012/12/13 16:22:48]

I used a PrefChangeRegistrary because I want to access the pref's IsDefault(), a
method that IntegerPrefMember does not provide. I am using this method to check
whether a session limit has been set. Alternatives would be:
* Check whether the current value is != 0. This is checking for magic values =>
bad.
* Check for IsManaged() instead => makes it impossible to just specify a limit
via prefs. Granted, nobody ever will but if it works, why break it?
* Extend IntegerPrefMember to provide IsDefault() => can do if you if want me
to.

+
+  base::RepeatingTimer<SessionLengthLimiter> repeating_timer_;
+  base::Time session_start_time_;
+  base::TimeDelta session_length_limit_;
+  ObserverList<Observer> observers_;
+
+  void OnSessionLengthLimitChanged();
+
+  void StartTimer();
+  void StopTimer();
+  void TimerTick();

[Mattias Nissler (ping if slow), 2012/12/12 10:12:57]

These functions could use some commenting on what they do.

[bartfab (slow), 2012/12/13 16:22:48]

Done.

+
+  scoped_ptr<base::TimeDelta> GetRemainingTime() const;
+
+  DISALLOW_COPY_AND_ASSIGN(SessionLengthLimiter);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_