Oobe: allow guest button in user creation screen

Allow browse as guest button to be shown in user creation screen in oobe.
Hide browse as guest button in user creation screen during add person flow.

Bug: 1101318
Change-Id: I235cbf486f11f3b0275adec3f44cdb9c31adb945
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2341640
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Denis Kuznetsov [CET] <antrim@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795977}

ash/shelf/login_shelf_view.cc

@@ -251,7 +251,8 @@ void StartAddUser() {
 
 bool DialogStateGuestAllowed(OobeDialogState state) {
   return state == OobeDialogState::GAIA_SIGNIN ||
-         state == OobeDialogState::ERROR || state == OobeDialogState::HIDDEN;
+         state == OobeDialogState::ERROR || state == OobeDialogState::HIDDEN ||
+         state == OobeDialogState::USER_CREATION;
 }
 
 bool ShutdownButtonHidden(OobeDialogState state) {
@@ -861,7 +862,8 @@ bool LoginShelfView::ShouldShowGuestButton() const {
   if (session_state != SessionState::LOGIN_PRIMARY)
     return false;
 
-  if (dialog_state_ == OobeDialogState::GAIA_SIGNIN)
+  if (dialog_state_ == OobeDialogState::USER_CREATION ||
+      dialog_state_ == OobeDialogState::GAIA_SIGNIN)
     return !login_screen_has_users_ && allow_guest_in_oobe_;
 
   return true;