chromeos: Convert system tray session length limit to mojo

ash/session/session_observer.h

 // Copyright (c) 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 ASH_SESSION_SESSION_OBSERVER_H_
 #define ASH_SESSION_SESSION_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "components/session_manager/session_manager_types.h"
@@ skipping 20 matching lines @@
 
   // Called when the login status is changed. |login_status| is the new status.
   virtual void OnLoginStatusChanged(LoginStatus login_status) {}
 
   // Called when the lock state is changed. |locked| is the current lock stated.
   virtual void OnLockStateChanged(bool locked) {}
 
   // Called when chrome is terminating.
   virtual void OnChromeTerminating() {}
 
+  // Called when the limit becomes available and when it changes.
+  virtual void OnSessionLengthLimitChanged() {}
+
  protected:
   virtual ~SessionObserver() {}
 };
 
 // A class to attach / detach an object as a session state observer.
 class ASH_EXPORT ScopedSessionObserver {
  public:
   explicit ScopedSessionObserver(SessionObserver* observer);
   virtual ~ScopedSessionObserver();
 
  private:
   SessionObserver* const observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedSessionObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SESSION_SESSION_OBSERVER_H_