Migrate //chromeos/ash/services/assistant to namespace ash [2/N]

This CL migrates public/cpp to namespace ash from chromeos. To avoid
conflicts with internal sources, this CL has temporary 'using'
declarations.

This CL is part of the Chrome OS source code directory migration:
https://docs.google.com/document/d/1g-98HpzA8XcoGBWUv1gQNr4rbnD5yfvbtYZyPDDbkaE.

Change-Id: I4e406d2a446c0bfe9f24fdfe9f3feab9e6026eff
Bug: 1164001
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3789017
Reviewed-by: Tao Wu <[email protected]>
Commit-Queue: Yeunjoo Choi <[email protected]>
Reviewed-by: Hidehiko Abe <[email protected]>
Owners-Override: Hidehiko Abe <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1030408}
diff --git a/chrome/browser/prefs/browser_prefs.cc b/chrome/browser/prefs/browser_prefs.cc
index b290799..5fe15ec 100644
--- a/chrome/browser/prefs/browser_prefs.cc
+++ b/chrome/browser/prefs/browser_prefs.cc
@@ -1511,7 +1511,7 @@
   ash::ApkWebAppService::RegisterProfilePrefs(registry);
   ash::app_time::AppActivityRegistry::RegisterProfilePrefs(registry);
   ash::app_time::AppTimeController::RegisterProfilePrefs(registry);
-  chromeos::assistant::prefs::RegisterProfilePrefs(registry);
+  ash::assistant::prefs::RegisterProfilePrefs(registry);
   ash::bluetooth::DebugLogsManager::RegisterPrefs(registry);
   chromeos::bluetooth_config::BluetoothPowerControllerImpl::
       RegisterProfilePrefs(registry);