Use only timezone IDs from known timezone list.

chrome/browser/chromeos/dom_ui/system_settings_provider.h

 // Copyright (c) 2010 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 CHROME_BROWSER_CHROMEOS_DOM_UI_SYSTEM_SETTINGS_PROVIDER_H_
 #define CHROME_BROWSER_CHROMEOS_DOM_UI_SYSTEM_SETTINGS_PROVIDER_H_
 
 #include <vector>
 
 #include "base/string16.h"
@@ skipping 28 matching lines @@
 
   // Gets timezone name.
   static string16 GetTimezoneName(const icu::TimeZone& timezone);
 
   // Gets timezone ID which is also used as timezone pref value.
   static string16 GetTimezoneID(const icu::TimeZone& timezone);
 
   // Gets timezone object from its id.
   const icu::TimeZone* GetTimezone(const string16& timezone_id);
 
+  // Gets a timezone id from a timezone in |timezones_| that has the same
+  // rule of given |timezone|.
+  // One timezone could have multiple timezones,
+  // e.g.
+  //   US/Pacific == America/Los_Angeles
+  // We should always use the known timezone id when passing back as
+  // pref values.
+  string16 GetKnownTimezoneID(const icu::TimeZone& timezone) const;
+
   // Timezones.
   std::vector<icu::TimeZone*> timezones_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemSettingsProvider);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_DOM_UI_SYSTEM_SETTINGS_PROVIDER_H_