Clarified description of the timezone policy.

chrome/browser/policy/proto/chrome_device_policy.proto

 // 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package enterprise_management;
 
@@ skipping 189 matching lines @@
   repeated ConnectionType allowed_connection_types = 5;
 }
 
 message StartUpUrlsProto {
   // Specifies the URLs to be loaded on login to the anonymous account used if
   // the device is in RETAIL mode.
   repeated string start_up_urls = 1;
 }
 
 message SystemTimezoneProto {
-  // Specifies the timezone which is applied if this value is provided. Valid
-  // values are listed in "timezone_settings.cc". Additionally, timezones from
-  // the "IANA Time Zone Database" (e.g. listed on wikipedia) that are
-  // equivalent to one of the timezones in "timezone_settings.cc" are valid.
+  // Specifies an owner-determined timezone that applies to the login screen and
+  // all users. Valid values are listed in "timezone_settings.cc". Additionally,
+  // timezones from the "IANA Time Zone Database" (e.g. listed on wikipedia)
+  // that are equivalent to one of the timezones in "timezone_settings.cc" are
+  // valid. In case of an invalid value (e.g. the empty string), the setting is
+  // still activated with a fallback timezone (currently "GMT").
+  // Only if no value is provided, the timezone device setting is inactive. In
+  // that case, the currently active timezone will remain in use however users
+  // can change the timezone and the change is persistent. Thus a change by one
+  // user affects the login-screen and all other users.
   optional string timezone = 1;
 }
 
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
   optional GuestModeEnabledProto guest_mode_enabled = 3;
   optional DeviceProxySettingsProto device_proxy_settings = 4;
   optional CameraEnabledProto camera_enabled = 5;
   optional ShowUserNamesOnSigninProto show_user_names = 6;
   optional DataRoamingEnabledProto data_roaming_enabled = 7;
   optional AllowNewUsersProto allow_new_users = 8;
   optional MetricsEnabledProto metrics_enabled = 9;
   optional ReleaseChannelProto release_channel = 10;
   optional DeviceOpenNetworkConfigurationProto open_network_configuration = 11;
   optional DeviceReportingProto device_reporting = 12;
   optional EphemeralUsersEnabledProto ephemeral_users_enabled = 13;
   optional AppPackProto app_pack = 14;
   optional ForcedLogoutTimeoutsProto forced_logout_timeouts = 15;
   optional ScreenSaverProto login_screen_saver = 16;
   optional AutoUpdateSettingsProto auto_update_settings = 17;
   optional StartUpUrlsProto start_up_urls = 18;
   optional PinnedAppsProto pinned_apps = 19;
   optional SystemTimezoneProto system_timezone = 20;
 }