Fix 'except' and 'prefer' spelling.

chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc

Index: chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc
diff --git a/chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc b/chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc
index 14f12be93f01d637167cb256b86888b9f34c1ea9..9c9de92b83f593f649bc19a483eaab412db35aef 100644
--- a/chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc
+++ b/chrome/browser/ui/ash/multi_user/user_switch_animator_chromeos.cc
@@ -186,7 +186,7 @@ void UserSwichAnimatorChromeOS::TransitionUserShelf(
          iter != root_windows.end(); ++iter) {
       // This shelf change is only part of the animation and will be updated by
       // ChromeLauncherController::ActiveUserChanged() to the new users value.
-      // Note that the user perference will not be changed.
+      // Note that the user preference will not be changed.
       ash::Shell::GetInstance()->SetShelfAutoHideBehavior(
           ash::SHELF_AUTO_HIDE_ALWAYS_HIDDEN, *iter);
     }