ash: Take the 24h clock pref into consideration when showing the time.

ash/system/tray/system_tray_delegate.h

Index: ash/system/tray/system_tray_delegate.h
diff --git a/ash/system/tray/system_tray_delegate.h b/ash/system/tray/system_tray_delegate.h
index de2b3886cba43d6de0849d322ff0cc8f46b0091f..40e6b077cc8b38b62bd15054fe52abffe45e1820 100644
--- a/ash/system/tray/system_tray_delegate.h
+++ b/ash/system/tray/system_tray_delegate.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "ash/system/user/login_status.h"
+#include "base/i18n/time_formatting.h"
 #include "base/string16.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
@@ -36,6 +37,9 @@ class SystemTrayDelegate {
   // Returns the resource id for the icon to show for the update notification.
   virtual int GetSystemUpdateIconResource() const = 0;
 
+  // Returns the desired hour clock type.
+  virtual base::HourClockType GetHourClockType() const = 0;
+
   // Shows settings.
   virtual void ShowSettings() = 0;