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

ash/system/power/date_format_observer.h

Index: ash/system/power/date_format_observer.h
diff --git a/ash/system/power/date_format_observer.h b/ash/system/power/date_format_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..dd45a4f630a504c3feac088b5e1eed4a95850ca6
--- /dev/null
+++ b/ash/system/power/date_format_observer.h
@@ -0,0 +1,19 @@
+// 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.
+
+#ifndef ASH_SYSTEM_POWER_DATE_FORMAT_OBSERVER_H_
+#define ASH_SYSTEM_POWER_DATE_FORMAT_OBSERVER_H_
+
+namespace ash {
+
+class DateFormatObserver {
+ public:
+  virtual ~DateFormatObserver() {}
+
+  virtual void OnDateFormatChanged() = 0;
+};
+
+};
+
+#endif  // ASH_SYSTEM_POWER_DATE_FORMAT_OBSERVER_H_