chromeos: Speculative fix for segfault with missing owner.

Try to avoid a crash in a situation we've seen where a lab
system has a policy file referencing an owner but the user
list in the Local State file is empty.

Bug: 850139
Change-Id: I4fad13685d8a8975e6b8f1e41a65bf37cdfcd89d
Reviewed-on: https://chromium-review.googlesource.com/1121377Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#572221}

chrome/browser/chromeos/login/users/chrome_user_manager_util.cc

@@ -113,10 +113,15 @@ bool AreSupervisedUsersAllowed(const CrosSettings* cros_settings) {
 bool IsGuestSessionAllowed(const CrosSettings* cros_settings) {
   const AccountId& owner_account_id =
       user_manager::UserManager::Get()->GetOwnerAccountId();
-  if (owner_account_id.is_valid() &&
-      user_manager::UserManager::Get()->FindUser(owner_account_id)->GetType() ==
-          user_manager::UserType::USER_TYPE_CHILD) {
-    return false;
+  if (owner_account_id.is_valid()) {
+    // Some Autotest policy tests appear to wipe the user list in Local State
+    // but preserve a policy file referencing an owner: https://crbug.com/850139
+    const user_manager::User* owner_user =
+        user_manager::UserManager::Get()->FindUser(owner_account_id);
+    if (owner_user &&
+        owner_user->GetType() == user_manager::UserType::USER_TYPE_CHILD) {
+      return false;
+    }
   }
 
   // In tests CrosSettings might not be initialized.

chrome/browser/ui/webui/chromeos/login/gaia_screen_handler.cc

@@ -413,10 +413,15 @@ void GaiaScreenHandler::LoadGaiaWithPartitionAndVersionAndConsent(
   const AccountId& owner_account_id =
       user_manager::UserManager::Get()->GetOwnerAccountId();
   params.SetBoolean("hasDeviceOwner", owner_account_id.is_valid());
-  if (owner_account_id.is_valid() &&
-      user_manager::UserManager::Get()->FindUser(owner_account_id)->GetType() ==
-          user_manager::UserType::USER_TYPE_CHILD) {
-    params.SetString("obfuscatedOwnerId", owner_account_id.GetGaiaId());
+  if (owner_account_id.is_valid()) {
+    // Some Autotest policy tests appear to wipe the user list in Local State
+    // but preserve a policy file referencing an owner: https://crbug.com/850139
+    const user_manager::User* owner_user =
+        user_manager::UserManager::Get()->FindUser(owner_account_id);
+    if (owner_user &&
+        owner_user->GetType() == user_manager::UserType::USER_TYPE_CHILD) {
+      params.SetString("obfuscatedOwnerId", owner_account_id.GetGaiaId());
+    }
   }
 
   params.SetString("chromeType", GetChromeType());