ChromeOS: implement per-user time zone preferences.

chrome/common/pref_names.h

Index: chrome/common/pref_names.h
diff --git a/chrome/common/pref_names.h b/chrome/common/pref_names.h
index 0bfb05b0c2d944c87300ef63ba3553b03020ebf4..f4928d606f48ea15191b0aff8df0c16a13573f1d 100644
--- a/chrome/common/pref_names.h
+++ b/chrome/common/pref_names.h
@@ -208,6 +208,7 @@ extern const char kPrimaryMouseButtonRight[];
 extern const char kMouseSensitivity[];
 extern const char kTouchpadSensitivity[];
 extern const char kUse24HourClock[];
+extern const char kUserTimezone[];
 extern const char kResolveTimezoneByGeolocation[];
 // TODO(yusukes): Change "kLanguageABC" to "kABC". The current form is too long
 // to remember and confusing. The prefs are actually for input methods and i18n
@@ -758,6 +759,7 @@ extern const char kFactoryResetRequested[];
 extern const char kDebuggingFeaturesRequested[];
 
 #if defined(OS_CHROMEOS)
+extern const char kSigninScreenTimezone[];
 extern const char kResolveDeviceTimezoneByGeolocation[];
 extern const char kSystemTimezoneAutomaticDetectionPolicy[];
 #endif  // defined(OS_CHROMEOS)