Add countdown when session time is limited

ash/system/session_length_limit/tray_session_length_limit.h

Index: ash/system/session_length_limit/tray_session_length_limit.h
diff --git a/ash/system/session_length_limit/tray_session_length_limit.h b/ash/system/session_length_limit/tray_session_length_limit.h
new file mode 100644
index 0000000000000000000000000000000000000000..0ee3f07e8fd6201b702e98a1faf92b6cc8baadd9
--- /dev/null
+++ b/ash/system/session_length_limit/tray_session_length_limit.h
@@ -0,0 +1,48 @@
+// 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_TRAY_SESSION_LENGTH_LIMIT_H_
+#define ASH_SYSTEM_SESSION_LENGTH_LIMIT_TRAY_SESSION_LENGTH_LIMIT_H_
+
+#include "ash/system/session_length_limit/session_length_limit_observer.h"
+#include "ash/system/tray/system_tray_item.h"
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+
+namespace ash {
+namespace internal {
+
+namespace tray {
+class RemainingSessionTimeTrayView;
+}
+
+// Adds a countdown timer to the system tray if the session length is limited.
+class TraySessionLengthLimit : public SystemTrayItem,
+                               public SessionLengthLimitObserver {
+ public:
+  explicit TraySessionLengthLimit(SystemTray* system_tray);
+  virtual ~TraySessionLengthLimit();
+
+  // SystemTrayItem:
+  virtual views::View* CreateTrayView(user::LoginStatus status) OVERRIDE;
+  virtual void DestroyTrayView() OVERRIDE;
+  virtual void UpdateAfterShelfAlignmentChange(
+      ShelfAlignment alignment) OVERRIDE;
+
+  // SessionLengthLimitObserver:
+  virtual void OnSessionStartTimeChanged(
+      const base::Time& start_time) OVERRIDE;
+  virtual void OnSessionLengthLimitChanged(
+      const base::TimeDelta& limit) OVERRIDE;
+
+ private:
+  tray::RemainingSessionTimeTrayView* tray_view_;
+
+  DISALLOW_COPY_AND_ASSIGN(TraySessionLengthLimit);
+};
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_SESSION_LENGTH_LIMIT_TRAY_SESSION_LENGTH_LIMIT_H_