Hook up system clock update dbus signal to chrome and ash tray ui.

ash/system/date/tray_date.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/date/tray_date.h"
 
 #include "ash/shell.h"
 #include "ash/system/date/date_view.h"
 #include "ash/system/tray/system_tray.h"
 #include "ash/system/tray/system_tray_delegate.h"
@@ skipping 170 matching lines @@
             HORIZONTAL_CLOCK : VERTICAL_CLOCK;
     time_tray_->UpdateClockLayout(clock_layout);
   }
 }
 
 void TrayDate::OnDateFormatChanged() {
   if (time_tray_)
     time_tray_->UpdateTimeFormat();
 }
 
+void TrayDate::OnSystemClockTimeUpdated() {
+  if (time_tray_)
+    time_tray_->UpdateTimeFormat();
+}
+
 void TrayDate::Refresh() {
   if (time_tray_)
     time_tray_->UpdateText();
 }
 
 }  // namespace internal
 }  // namespace ash