Basic UkmService implementation

components/metrics/metrics_service_client.cc

 // Copyright 2014 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 "components/metrics/metrics_service_client.h"
 
 #include "components/metrics/url_constants.h"
 
 namespace metrics {
 
+ukm::UkmService* MetricsServiceClient::GetUkmService() {
+  return nullptr;
+}
+
 base::string16 MetricsServiceClient::GetRegistryBackupKey() {
   return base::string16();
 }
 
 bool MetricsServiceClient::IsReportingPolicyManaged() {
   return false;
 }
 
 EnableMetricsDefault MetricsServiceClient::GetMetricsReportingDefaultState() {
   return EnableMetricsDefault::DEFAULT_UNKNOWN;
 }
 
 bool MetricsServiceClient::IsUMACellularUploadLogicEnabled() {
   return false;
 }
 
 std::string MetricsServiceClient::GetMetricsServerUrl() {
   return metrics::kDefaultMetricsServerUrl;
 }
 
 }  // namespace metrics