Add UKM initial_url and session_id fields.

components/ukm/ukm_service.h

 // 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.
 
 #ifndef COMPONENTS_UKM_UKM_SERVICE_H_
 #define COMPONENTS_UKM_UKM_SERVICE_H_
 
 #include <stddef.h>
 #include <memory>
 #include <vector>
@@ skipping 140 matching lines @@
 
   // A weak pointer to the PrefService used to read and write preferences.
   PrefService* pref_service_;
 
   // Whether recording new data is currently allowed.
   bool recording_enabled_;
 
   // The UKM client id stored in prefs.
   uint64_t client_id_;
 
+  // The UKM session id stored in prefs.
+  int32_t session_id_;
+
   // Used to interact with the embedder. Weak pointer; must outlive |this|
   // instance.
   metrics::MetricsServiceClient* const client_;
 
   // Registered metrics providers.
   std::vector<std::unique_ptr<metrics::MetricsProvider>> metrics_providers_;
 
   // Logs that have not yet been sent.
   metrics::PersistedLogs persisted_logs_;
 
@@ skipping 18 matching lines @@
   // Weak pointers factory used to post task on different threads. All weak
   // pointers managed by this factory have the same lifetime as UkmService.
   base::WeakPtrFactory<UkmService> self_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UkmService);
 };
 
 }  // namespace ukm
 
 #endif  // COMPONENTS_UKM_UKM_SERVICE_H_