Add countdown when session time is limited

ash/system/session_length_limit/session_length_limit_observer.h

Index: ash/system/session_length_limit/session_length_limit_observer.h
diff --git a/ash/system/session_length_limit/session_length_limit_observer.h b/ash/system/session_length_limit/session_length_limit_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..29b7bb35751e4b75c08ad2a491580d611b7326d4
--- /dev/null
+++ b/ash/system/session_length_limit/session_length_limit_observer.h
@@ -0,0 +1,27 @@
+// 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 ASH_SYSTEM_SESSION_LENGTH_LIMIT_SESSION_LENGTH_LIMIT_OBSERVER_H_
+#define ASH_SYSTEM_SESSION_LENGTH_LIMIT_SESSION_LENGTH_LIMIT_OBSERVER_H_
+
+#include "base/time.h"
+
+namespace ash {
+
+// Observer for the remaining session time, if limited by policy.
+class SessionLengthLimitObserver {
+ public:
+  virtual ~SessionLengthLimitObserver() {}
+
+  // Called when the session length limit is removed.
+  virtual void OnSessionLengthUnlimited() = 0;
+
+  // Called once per second when the session length limit is limited.
+  virtual void OnRemainingSessionTimeChanged(
+      const base::TimeDelta& remaining) = 0;

[stevenjb, 2012/12/14 18:02:21]

This really needs to be OnSessionExpiredTimeChanged(), otherwise the countdown
could be uneven which would look really strange.

[bartfab (slow), 2012/12/14 20:11:09]

Changed to use an internal periodic timer.

+};
+
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_SESSION_LENGTH_LIMIT_SESSION_LENGTH_LIMIT_OBSERVER_H_