chromeos: Convert system tray session length limit to mojo

ash/system/session/tray_session_length_limit.h

 // Copyright 2014 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_TRAY_SESSION_LENGTH_LIMIT_H_
 #define ASH_SYSTEM_SESSION_TRAY_SESSION_LENGTH_LIMIT_H_
 
 #include <memory>
 
-#include "ash/system/session/session_length_limit_observer.h"
+#include "ash/session/session_observer.h"
 #include "ash/system/tray/system_tray_item.h"
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 
 namespace ash {
 namespace test {
 class TraySessionLengthLimitTest;
 }
 
 class LabelTrayView;
 
 // Adds a countdown timer to the system tray if the session length is limited.
 class ASH_EXPORT TraySessionLengthLimit : public SystemTrayItem,
-                                          public SessionLengthLimitObserver {
+                                          public SessionObserver {
  public:
   enum LimitState { LIMIT_NONE, LIMIT_SET, LIMIT_EXPIRING_SOON };
 
   explicit TraySessionLengthLimit(SystemTray* system_tray);
   ~TraySessionLengthLimit() override;
 
   // SystemTrayItem:
   views::View* CreateDefaultView(LoginStatus status) override;
   void OnDefaultViewDestroyed() override;
 
-  // SessionLengthLimitObserver:
-  void OnSessionStartTimeChanged() override;
+  // SessionObserver:
   void OnSessionLengthLimitChanged() override;
 
  private:
   friend class test::TraySessionLengthLimitTest;
 
   static const char kNotificationId[];
 
   // Update state, notification and tray bubble view.  Called by the
   // RepeatingTimer in regular intervals and also by OnSession*Changed().
   void Update();
 
   // Recalculate |limit_state_| and |remaining_session_time_|.
   void UpdateState();
 
   void UpdateNotification();
   void UpdateTrayBubbleView() const;
 
   // These require that the state has been updated before.
   base::string16 ComposeNotificationMessage() const;
   base::string16 ComposeTrayBubbleMessage() const;
 
-  base::TimeTicks session_start_time_;
-  base::TimeDelta time_limit_;
   base::TimeDelta remaining_session_time_;
 
   LimitState limit_state_;       // Current state.
   LimitState last_limit_state_;  // State of last notification update.
 
   LabelTrayView* tray_bubble_view_;
   std::unique_ptr<base::RepeatingTimer> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(TraySessionLengthLimit);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_SESSION_TRAY_SESSION_LENGTH_LIMIT_H_