We should use UserID object to identify users instead of username.

chrome/browser/ui/webui/options/chromeos/accounts_options_handler.cc

 // 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.
 
 #include "chrome/browser/ui/webui/options/chromeos/accounts_options_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 103 matching lines @@
     WhitelistUser(service, gaia::CanonicalizeEmail(typed_email));
   }
 }
 
 void AccountsOptionsHandler::HandleUnwhitelistUser(
     const base::ListValue* args) {
   std::string email;
   if (!args->GetString(0, &email)) {
     return;
   }
+  const user_manager::UserID user_id(user_manager::UserID::FromUserEmail(gaia::CanonicalizeEmail(email)));
 
-  base::StringValue canonical_email(gaia::CanonicalizeEmail(email));
+  base::StringValue canonical_email(user_id.GetUserEmail());
   if (OwnerSettingsServiceChromeOS* service =
           OwnerSettingsServiceChromeOS::FromWebUI(web_ui())) {
     service->RemoveFromList(kAccountsPrefUsers, canonical_email);
   }
-  user_manager::UserManager::Get()->RemoveUser(email, NULL);
+  user_manager::UserManager::Get()->RemoveUser(user_id, NULL);
 }
 
 void AccountsOptionsHandler::HandleUpdateWhitelist(
     const base::ListValue* args) {
   DCHECK(args && args->empty());
 
   // Creates one list to set. This is needed because user white list update is
   // asynchronous and sequential. Before previous write comes back, cached list
   // is stale and should not be used for appending. See http://crbug.com/127215
   scoped_ptr<base::ListValue> new_list;
@@ skipping 16 matching lines @@
       new_list->Remove(i, NULL);
       --i;
     }
   }
 
   const user_manager::UserList& users =
       user_manager::UserManager::Get()->GetUsers();
   for (user_manager::UserList::const_iterator it = users.begin();
        it < users.end();
        ++it)
-    new_list->AppendIfNotPresent(new base::StringValue((*it)->email()));
+    new_list->AppendIfNotPresent(new base::StringValue((*it)->GetUserID().GetUserEmail()));
 
   if (OwnerSettingsServiceChromeOS* service =
           OwnerSettingsServiceChromeOS::FromWebUI(web_ui())) {
     service->Set(kAccountsPrefUsers, *new_list.get());
   }
 }
 
 }  // namespace options
 }  // namespace chromeos