chromeos: Convert system tray session length limit to mojo

ash/session/session_controller.h

Index: ash/session/session_controller.h
diff --git a/ash/session/session_controller.h b/ash/session/session_controller.h
index 7f6cd864bbbd81fa159e3f0b131a775c9ea360f4..392aa7c495f7e6207e7d8c9881804794159cffef 100644
--- a/ash/session/session_controller.h
+++ b/ash/session/session_controller.h
@@ -17,6 +17,7 @@
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list.h"
+#include "base/time/time.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 
 class AccountId;
@@ -34,6 +35,9 @@ class ASH_EXPORT SessionController
   SessionController();
   ~SessionController() override;
 
+  base::TimeDelta session_length_limit() const { return session_length_limit_; }
+  base::TimeTicks session_start_time() const { return session_start_time_; }
+
   // Binds the mojom::SessionControllerRequest to this object.
   void BindRequest(mojom::SessionControllerRequest request);
 
@@ -124,6 +128,8 @@ class ASH_EXPORT SessionController
   void NotifyChromeLockAnimationsComplete() override;
   void RunUnlockAnimation(RunUnlockAnimationCallback callback) override;
   void NotifyChromeTerminating() override;
+  void SetSessionLengthLimit(base::TimeDelta length_limit,
+                             base::TimeTicks start_time) override;
 
   // Test helpers.
   void ClearUserSessionsForTest();
@@ -180,6 +186,14 @@ class ASH_EXPORT SessionController
   // Pending callback for the StartLock request.
   base::OnceCallback<void(bool)> start_lock_callback_;
 
+  // Zero if there is no session length limit.

[msw, 2017/06/06 19:01:04]

nit: "The session length limit; set to zero if there is no limit."

[James Cook, 2017/06/07 00:48:13]

Done.

+  base::TimeDelta session_length_limit_;
+
+  // Stored in a pref in case of a crash in the middle of the session. Can

[msw, 2017/06/06 19:01:04]

nit: "The session start time, set at login or on the first user activity; set to
null if there is no session length limit. This value is also stored in a pref in
case of a crash during the session."

[James Cook, 2017/06/07 00:48:13]

Done.

+  // either be login time or the time of first user activity. Null when there
+  // is no session length limit.
+  base::TimeTicks session_start_time_;
+
   base::ObserverList<ash::SessionObserver> observers_;
 
   base::WeakPtrFactory<SessionController> weak_ptr_factory_;