Convert first contentful paint logging to the new UKM client API

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 65 matching lines @@
 
   // Registers the specified |provider| to provide additional metrics into the
   // UKM log. Should be called during MetricsService initialization only.
   void RegisterMetricsProvider(
       std::unique_ptr<metrics::MetricsProvider> provider);
 
   // Registers the names of all of the preferences used by UkmService in
   // the provided PrefRegistry.
   static void RegisterPrefs(PrefRegistrySimple* registry);
 
+  // Allocates a new source id. The allocated source id is guaranteed to be
+  // unique for the duration of this browser session.
+  static int32_t NewSourceId();
+
   using AddEntryCallback = base::Callback<void(std::unique_ptr<UkmEntry>)>;
 
  protected:
   const std::vector<std::unique_ptr<UkmSource>>& sources_for_testing() const {
     return sources_;
   }
 
+  const std::vector<std::unique_ptr<UkmEntry>>& entries_for_testing() const {
+    return entries_;
+  }
+
  private:
   friend UkmPageLoadMetricsObserver;
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, AddEntryOnlyWithNonEmptyMetrics);
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, EntryBuilderAndSerialization);
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest,
                            LogsUploadedOnlyWhenHavingSourcesOrEntries);
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, MetricsProviderTest);
   FRIEND_TEST_ALL_PREFIXES(UkmServiceTest, PersistAndPurge);
 
   // Get a new UkmEntryBuilder object for the specified source ID and event,
@@ skipping 73 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_