[CrOS Settings] Move synced wallpaper pref.

In [1], treib@ suggested moving this to settings pref instead of
including it within sync prefs.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1977956

Change-Id: Ide9c1c4e8b1ede12e3324db96db44293bc8ec703
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008302
Commit-Queue: Kyle Horimoto <[email protected]>
Reviewed-by: Marc Treib <[email protected]>
Cr-Commit-Position: refs/heads/master@{#734273}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index ba79fe4..1ee3be64 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -314,6 +314,7 @@
 #include "chrome/browser/ui/webui/chromeos/login/enable_debugging_screen_handler.h"
 #include "chrome/browser/ui/webui/chromeos/login/hid_detection_screen_handler.h"
 #include "chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h"
+#include "chrome/browser/ui/webui/settings/chromeos/os_settings_ui.h"
 #include "chrome/browser/upgrade_detector/upgrade_detector_chromeos.h"
 #include "chromeos/audio/audio_devices_pref_handler_impl.h"
 #include "chromeos/components/account_manager/account_manager.h"
@@ -978,6 +979,7 @@
   chromeos::RegisterSamlProfilePrefs(registry);
   chromeos::ScreenTimeController::RegisterProfilePrefs(registry);
   chromeos::ServicesCustomizationDocument::RegisterProfilePrefs(registry);
+  chromeos::settings::OSSettingsUI::RegisterProfilePrefs(registry);
   chromeos::UserImageSyncObserver::RegisterProfilePrefs(registry);
   crostini::prefs::RegisterProfilePrefs(registry);
   chromeos::attestation::TpmChallengeKey::RegisterProfilePrefs(registry);