Add UKM API GetNewSourceID()

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 31 matching lines @@
 // uploading reports that contain fine grained performance metrics including
 // URLs for top-level navigations.
 class UkmService : public base::SupportsWeakPtr<UkmService> {
  public:
   // Constructs a UkmService.
   // Calling code is responsible for ensuring that the lifetime of
   // |pref_service| is longer than the lifetime of UkmService.
   UkmService(PrefService* pref_service, metrics::MetricsServiceClient* client);
   virtual ~UkmService();
 
+  // Get the new source ID, which is unique for the duration of a browser
+  // session.
+  static int32_t GetNewSourceID();
+
   // Update the URL on the source keyed to the given source ID. If the source
   // does not exist, it will create a new UkmSource object.
   void UpdateSourceURL(int32_t source_id, const GURL& url);
 
   // Initializes the UKM service.
   void Initialize();
 
   // Enables/disables recording control if data is allowed to be collected.
   void EnableRecording();
   void DisableRecording();
@@ skipping 114 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_