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

chrome/browser/chromeos/accessibility/accessibility_manager.cc

 // Copyright (c) 2013 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/accessibility/accessibility_manager.h"
 
 #include "ash/audio/sounds.h"
 #include "ash/autoclick/autoclick_controller.h"
 #include "ash/high_contrast/high_contrast_controller.h"
 #include "ash/metrics/user_metrics_recorder.h"
@@ skipping 910 matching lines @@
     UpdateBrailleImeState();
   UpdateLargeCursorFromPref();
   UpdateStickyKeysFromPref();
   UpdateSpokenFeedbackFromPref();
   UpdateHighContrastFromPref();
   UpdateAutoclickFromPref();
   UpdateAutoclickDelayFromPref();
   UpdateVirtualKeyboardFromPref();
 }
 
-void AccessibilityManager::ActiveUserChanged(const std::string& user_id) {
+void AccessibilityManager::ActiveUserChanged(const user_manager::UserID& user_id) {
   SetProfile(ProfileManager::GetActiveUserProfile());
 }
 
 void AccessibilityManager::SetProfileForTest(Profile* profile) {
   SetProfile(profile);
 }
 
 void AccessibilityManager::SetBrailleControllerForTest(
     BrailleController* controller) {
   g_braille_controller_for_test = controller;
@@ skipping 170 matching lines @@
 void AccessibilityManager::PostUnloadChromeVox(Profile* profile) {
   // Do any teardown work needed immediately after ChromeVox actually unloads.
   if (system_sounds_enabled_)
     ash::PlaySystemSoundAlways(SOUND_SPOKEN_FEEDBACK_DISABLED);
   // Clear the accessibility focus ring.
   AccessibilityFocusRingController::GetInstance()->SetFocusRing(
       std::vector<gfx::Rect>());
 }
 
 }  // namespace chromeos