chromeos: Convert system tray session length limit to mojo

ash/system/tray/system_tray_delegate.cc

 // 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.
 
 #include "ash/system/tray/system_tray_delegate.h"
 
 #include "ash/system/tray/ime_info.h"
 
 namespace ash {
 
@@ skipping 13 matching lines @@
 
 base::string16 SystemTrayDelegate::GetIMEManagedMessage() {
   return base::string16();
 }
 
 NetworkingConfigDelegate* SystemTrayDelegate::GetNetworkingConfigDelegate()
     const {
   return nullptr;
 }
 
-bool SystemTrayDelegate::GetSessionStartTime(
-    base::TimeTicks* session_start_time) {
-  return false;
-}
-
-bool SystemTrayDelegate::GetSessionLengthLimit(
-    base::TimeDelta* session_length_limit) {
-  return false;
-}
-
 void SystemTrayDelegate::ActiveUserWasChanged() {}
 
 bool SystemTrayDelegate::IsSearchKeyMappedToCapsLock() {
   return false;
 }
 
 }  // namespace ash