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

chrome/browser/chromeos/profiles/multiprofiles_session_aborted_dialog.cc

 // Copyright 2014 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/chromeos/profiles/multiprofiles_session_aborted_dialog.h"
 
 #include "ash/shell.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/lifetime/application_lifetime.h"
 #include "chrome/grit/generated_resources.h"
+#include "components/user_manager/user_id.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/views/controls/button/checkbox.h"
 #include "ui/views/controls/label.h"
 #include "ui/views/layout/grid_layout.h"
 #include "ui/views/widget/widget.h"
 #include "ui/views/window/dialog_delegate.h"
 
 namespace chromeos {
 
 namespace {
 
 // Default width/height of the dialog.
 const int kDefaultWidth = 600;
 const int kDefaultHeight = 250;
 
 const int kPaddingToMessage = 20;
 const int kInset = 40;
 const int kTopInset = 10;
 
 ////////////////////////////////////////////////////////////////////////////////
 // Dialog for an aborted multi-profile session due to a user policy change .
 class MultiprofilesSessionAbortedView : public views::DialogDelegateView {
  public:
   explicit MultiprofilesSessionAbortedView();
   ~MultiprofilesSessionAbortedView() override;
 
-  static void ShowDialog(const std::string& user_email);
+  static void ShowDialog(const user_manager::UserID& user_email);
 
   // views::DialogDelegate overrides.
   bool Accept() override;
   int GetDialogButtons() const override;
   base::string16 GetDialogButtonLabel(ui::DialogButton button) const override;
 
   // views::WidgetDelegate overrides.
   ui::ModalType GetModalType() const override;
 
   // views::View overrides.
   gfx::Size GetPreferredSize() const override;
 
  private:
   void InitDialog(const std::string& user_email);
 
   DISALLOW_COPY_AND_ASSIGN(MultiprofilesSessionAbortedView);
 };
 
 ////////////////////////////////////////////////////////////////////////////////
 // MultiprofilesSessionAbortedView implementation.
 
 MultiprofilesSessionAbortedView::MultiprofilesSessionAbortedView() {
 }
 
 MultiprofilesSessionAbortedView::~MultiprofilesSessionAbortedView() {
 }
 
 // static
 void MultiprofilesSessionAbortedView::ShowDialog(
-    const std::string& user_email) {
+    const user_manager::UserID& user_id) {
   MultiprofilesSessionAbortedView* dialog_view =
       new MultiprofilesSessionAbortedView();
   views::DialogDelegate::CreateDialogWidget(
       dialog_view, ash::Shell::GetTargetRootWindow(), NULL);
-  dialog_view->InitDialog(user_email);
+  dialog_view->InitDialog(user_id.GetUserEmail());
   views::Widget* widget = dialog_view->GetWidget();
   DCHECK(widget);
   widget->Show();
 
   // Since this is the last thing the user ever sees, we also hide all system
   // tray's from the screen.
   aura::Window::Windows root_windows = ash::Shell::GetAllRootWindows();
   for (aura::Window::Windows::const_iterator iter = root_windows.begin();
        iter != root_windows.end(); ++iter) {
     ash::Shell::GetInstance()->SetShelfAutoHideBehavior(
@@ skipping 59 matching lines @@
 
   SetLayoutManager(grid_layout);
   Layout();
 }
 
 }  // namespace
 
 ////////////////////////////////////////////////////////////////////////////////
 // Factory function.
 
-void ShowMultiprofilesSessionAbortedDialog(const std::string& user_email) {
-  MultiprofilesSessionAbortedView::ShowDialog(user_email);
+void ShowMultiprofilesSessionAbortedDialog(const user_manager::UserID& user_id) {
+  MultiprofilesSessionAbortedView::ShowDialog(user_id);
 }
 
 }  // namespace chromeos