Remove non-MD code from TrayBackgroundView

ash/common/system/chromeos/session/logout_button_tray.h

Index: ash/common/system/chromeos/session/logout_button_tray.h
diff --git a/ash/common/system/chromeos/session/logout_button_tray.h b/ash/common/system/chromeos/session/logout_button_tray.h
index cc0d3746061fb41c85d82184fb0106172b5f234a..2e77455ec60522aa9cdd34a19bbdbe95f2af4d1c 100644
--- a/ash/common/system/chromeos/session/logout_button_tray.h
+++ b/ash/common/system/chromeos/session/logout_button_tray.h
@@ -21,6 +21,8 @@ namespace ash {
 
 // Adds a logout button to the launcher's status area if enabled by the
 // kShowLogoutButtonInTray pref.
+// TODO(mohsen): This is not using much of the TrayBackgroundView functionality.
+// Consider making this a regular View.
 class ASH_EXPORT LogoutButtonTray : public TrayBackgroundView,
                                     public LogoutButtonObserver {
  public: