Remove some ifdefs from ash since it only supports ChromeOS now.

ash/display/display_util.h

Index: ash/display/display_util.h
diff --git a/ash/display/display_util.h b/ash/display/display_util.h
index eb2176286eaebf058607567c7fd7fbccfa53ec93..0f60738be8ac339a222878309477d7496bbc3149 100644
--- a/ash/display/display_util.h
+++ b/ash/display/display_util.h
@@ -47,12 +47,10 @@ void MoveCursorTo(AshWindowTreeHost* ash_host,
                   const gfx::Point& point_in_screen,
                   bool update_last_location_now);
 
-#if defined(OS_CHROMEOS)
 // Shows the notification message for display related issues, and optionally
 // adds a button to send a feedback report.
 void ShowDisplayErrorNotification(const base::string16& message,
                                   bool allow_feedback);
-#endif
 
 ASH_EXPORT base::string16 GetDisplayErrorNotificationMessageForTest();