Fixed changes to timezones in managed guest sessions not taking effect

Timezone changes in managed guest sessions used to not take effect even
when the policy was set to allow for them. Now a policy check is done
instead. These changes will still not persist through logging out/rebooting,
as these are temporary sessions.

Bug: 907667
Change-Id: Ib4f92f46b9bc9119afd44eb067f9cba2acf2d1f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1869656Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Muhamed Parić <muhamedp@google.com>
Cr-Commit-Position: refs/heads/master@{#714191}

chrome/browser/chromeos/system/timezone_util.cc

@@ -151,6 +151,17 @@ base::string16 GetTimezoneName(const icu::TimeZone& timezone) {
   return result;
 }
 
+bool CanSetSystemTimezoneFromManagedGuestSession() {
+  const int automatic_detection_policy =
+      g_browser_process->local_state()->GetInteger(
+          prefs::kSystemTimezoneAutomaticDetectionPolicy);
+
+  return (automatic_detection_policy ==
+          enterprise_management::SystemTimezoneProto::DISABLED) ||
+         (automatic_detection_policy ==
+          enterprise_management::SystemTimezoneProto::USERS_DECIDE);
+}
+
 // Returns true if the given user is allowed to set the system timezone - that
 // is, the single timezone at TimezoneSettings::GetInstance()->GetTimezone(),
 // which is also stored in a file at /var/lib/timezone/localtime.
@@ -168,13 +179,15 @@ bool CanSetSystemTimezone(const user_manager::User* user) {
       return true;
 
     case user_manager::USER_TYPE_GUEST:
-    case user_manager::USER_TYPE_PUBLIC_ACCOUNT:
       return false;
 
     case user_manager::USER_TYPE_CHILD:
       return base::FeatureList::IsEnabled(
           features::kParentAccessCodeForTimeChange);
 
+    case user_manager::USER_TYPE_PUBLIC_ACCOUNT:
+      return CanSetSystemTimezoneFromManagedGuestSession();
+
     case user_manager::NUM_USER_TYPES:
       NOTREACHED();