Remove non-cros support from ash/common/system.

ash/common/system/date/tray_date.h

Index: ash/common/system/date/tray_date.h
diff --git a/ash/common/system/date/tray_date.h b/ash/common/system/date/tray_date.h
index 87f00b254f63b090095cc425bb4f91bf700252aa..bf25e617d664215d13204e01b3d032189d827a3d 100644
--- a/ash/common/system/date/tray_date.h
+++ b/ash/common/system/date/tray_date.h
@@ -15,9 +15,7 @@
 
 namespace ash {
 class DateDefaultView;
-#if defined(OS_CHROMEOS)
 class SystemClockObserver;
-#endif
 
 namespace tray {
 class TimeView;
@@ -68,9 +66,7 @@ class ASH_EXPORT TrayDate : public SystemTrayItem, public ClockObserver {
   DateDefaultView* default_view_;
   LoginStatus login_status_;
 
-#if defined(OS_CHROMEOS)
   std::unique_ptr<SystemClockObserver> system_clock_observer_;
-#endif
 
   DISALLOW_COPY_AND_ASSIGN(TrayDate);
 };