Switch base::Value typemapping to be by value instead of by unique_ptr.

services/preferences/public/cpp/pref_store_client.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/preferences/public/cpp/pref_store_client.h"
 
 #include <utility>
 
 namespace prefs {
 
 PrefStoreClient::PrefStoreClient(mojom::PrefStoreConnectionPtr connection) {
-  Init(std::move(connection->initial_prefs), connection->is_initialized,
+  Init(&connection->initial_prefs, connection->is_initialized,
        std::move(connection->observer));
 }
 
 PrefStoreClient::~PrefStoreClient() = default;
 
 }  // namespace prefs