Add SessionStateObserver with ActiveUserChanged()

ash/system/tray/system_tray.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.h"
 
 #include "ash/ash_switches.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shell.h"
 #include "ash/shell/panel_window.h"
@@ skipping 303 matching lines @@
            notification_bubble_->bubble()->IsVisible()));
 }
 
 bool SystemTray::IsMouseInNotificationBubble() const {
   if (!notification_bubble_)
     return false;
   return notification_bubble_->bubble_view()->GetBoundsInScreen().Contains(
       Shell::GetScreen()->GetCursorScreenPoint());
 }
 
-bool SystemTray::CloseSystemBubbleForTest() const {
+bool SystemTray::CloseSystemBubble() const {
   if (!system_bubble_)
     return false;
   system_bubble_->bubble()->Close();
   return true;
 }
 
 bool SystemTray::CloseNotificationBubbleForTest() const {
   if (!notification_bubble_)
     return false;
   notification_bubble_->bubble()->Close();
@@ skipping 241 matching lines @@
         ConvertPointToWidget(this, &point);
         arrow_offset = point.x();
       }
     }
     ShowDefaultViewWithOffset(BUBBLE_CREATE_NEW, arrow_offset);
   }
   return true;
 }
 
 }  // namespace ash