chromeos: Convert system tray session length limit to mojo

ash/system/tray/system_tray_delegate.h

Index: ash/system/tray/system_tray_delegate.h
diff --git a/ash/system/tray/system_tray_delegate.h b/ash/system/tray/system_tray_delegate.h
index c0e26deb1215c06be33633d78a3545e84719f846..81ba1b1362e10cafc47b962d7cb2d368b2c01a20 100644
--- a/ash/system/tray/system_tray_delegate.h
+++ b/ash/system/tray/system_tray_delegate.h
@@ -9,14 +9,8 @@
 #include <vector>
 
 #include "ash/ash_export.h"
-#include "base/i18n/time_formatting.h"
 #include "base/strings/string16.h"
 
-namespace base {
-class TimeDelta;
-class TimeTicks;
-}
-
 namespace ash {
 struct IMEInfo;
 struct IMEPropertyInfo;
@@ -59,12 +53,6 @@ class ASH_EXPORT SystemTrayDelegate {
   // Returns NetworkingConfigDelegate. May return nullptr.
   virtual NetworkingConfigDelegate* GetNetworkingConfigDelegate() const;
 
-  // Retrieves the session start time. Returns |false| if the time is not set.
-  virtual bool GetSessionStartTime(base::TimeTicks* session_start_time);
-
-  // Retrieves the session length limit. Returns |false| if no limit is set.
-  virtual bool GetSessionLengthLimit(base::TimeDelta* session_length_limit);
-
   // The active user has been changed. This will be called when the UI is ready
   // to be switched to the new user.
   // Note: This will happen after SessionObserver::ActiveUserChanged fires.