Merge ash/public/cpp/ash_pref_names.* into ash/constants/

ash/{public/cpp,constants}/ash_pref_names.* serve the same purpose. The
latter is now the proper directory to add preferences to.

Bug: 1164001
Change-Id: I260bac7a7a5b8b223bc81d47f91188025fe85861
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2949053
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Henrique Ferreiro <hferreiro@igalia.com>
Cr-Commit-Position: refs/heads/master@{#900771}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index 671ec86..70d7981 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -6,11 +6,11 @@
 
 #include <utility>
 
+#include "ash/constants/ash_pref_names.h"
 #include "ash/focus_cycler.h"
 #include "ash/login/security_token_request_controller.h"
 #include "ash/login/ui/lock_screen.h"
 #include "ash/login/ui/login_data_dispatcher.h"
-#include "ash/public/cpp/ash_pref_names.h"
 #include "ash/public/cpp/child_accounts/parent_access_controller.h"
 #include "ash/public/cpp/login_screen_client.h"
 #include "ash/public/cpp/toast_data.h"