Pref service: add persistent pref store frontend and backend.

services/preferences/public/cpp/tests/pref_store_client_unittest.cc

Index: services/preferences/public/cpp/tests/pref_store_client_unittest.cc
diff --git a/services/preferences/public/cpp/tests/pref_store_client_unittest.cc b/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
index 856bcb3fe72820e9749e5fa7ff9ae7de225bd466..5b2272765128d3d43f8a0d96266eb826c9896d76 100644
--- a/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
+++ b/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
@@ -43,7 +43,7 @@ class PrefStoreClientTest : public testing::Test {
   PrefStoreObserverMock& observer() { return observer_; }
   PrefStoreClient* store() { return store_.get(); }
 
-  bool initialized() { return store_->initialized_; }
+  bool initialized() { return store_->IsInitializationComplete(); }
   void OnPrefChanged(const std::string& key, const base::Value& value) {
     observer_ptr_->OnPrefChanged(key, value.CreateDeepCopy());
   }