Re-enable preferences service access for browser+ash

services/preferences/public/cpp/pref_client_store.cc

Index: services/preferences/public/cpp/pref_client_store.cc
diff --git a/services/preferences/public/cpp/pref_client_store.cc b/services/preferences/public/cpp/pref_client_store.cc
index 2ca813455408032c2f7caef7c9164bbda1706640..289aaaadd20fd276527dabc6930bdaadc4542b5d 100644
--- a/services/preferences/public/cpp/pref_client_store.cc
+++ b/services/preferences/public/cpp/pref_client_store.cc
@@ -82,7 +82,7 @@ void PrefClientStore::SetValueOnPreferenceManager(const std::string& key,
     return;
 
   auto prefs = base::MakeUnique<base::DictionaryValue>();
-  prefs->Set(key, value.CreateDeepCopy());
+  prefs->SetWithoutPathExpansion(key, value.CreateDeepCopy());
   prefs_service_ptr_->SetPreferences(std::move(prefs));
 }