Basic UkmService implementation

components/metrics/persisted_logs.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/persisted_logs.h"
 
 #include <memory>
 #include <string>
 #include <utility>
 
@@ skipping 78 matching lines @@
 }
 
 PersistedLogs::~PersistedLogs() {}
 
 void PersistedLogs::SerializeLogs() const {
   ListPrefUpdate update(local_state_, pref_name_);
   WriteLogsToPrefList(update.Get());
 
   // After writing all the logs to the new pref remove old outdated pref.
   // TODO(gayane): Remove when all users are migrated. crbug.com/649440
-  if (local_state_->HasPrefPath(outdated_pref_name_))
+  if (outdated_pref_name_ && local_state_->HasPrefPath(outdated_pref_name_))
     local_state_->ClearPref(outdated_pref_name_);
 }
 
 PersistedLogs::LogReadStatus PersistedLogs::DeserializeLogs() {
   // TODO(gayane): Remove the code for reading logs from outdated pref when all
   // users are migrated. crbug.com/649440
-  if (local_state_->HasPrefPath(outdated_pref_name_)) {
+  if (outdated_pref_name_ && local_state_->HasPrefPath(outdated_pref_name_)) {
     return ReadLogsFromOldFormatPrefList(
         *local_state_->GetList(outdated_pref_name_));
   }
   return ReadLogsFromPrefList(*local_state_->GetList(pref_name_));
 }
 
 void PersistedLogs::StoreLog(const std::string& log_data) {
   list_.push_back(LogInfo());
   list_.back().Init(metrics_.get(),
                     log_data,
@@ skipping 109 matching lines @@
         !ReadBase64String(list_value, i * 2 + 1, &list_[i].hash)) {
       list_.clear();
       return metrics_->RecordLogReadStatus(LOG_STRING_CORRUPTION);
     }
   }
 
   return metrics_->RecordLogReadStatus(RECALL_SUCCESS);
 }
 
 }  // namespace metrics