No 'prefs' state is necessary for an active file.

components/metrics/file_metrics_provider_unittest.cc

 // Copyright 2016 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/file_metrics_provider.h"
 
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
@@ skipping 354 matching lines @@
   CreateGlobalHistograms(2);
   ASSERT_TRUE(PathExists(metrics_file()));
   base::HistogramBase* h0 = GetCreatedHistogram(0);
   base::HistogramBase* h1 = GetCreatedHistogram(1);
   DCHECK(h0);
   DCHECK(h1);
   std::unique_ptr<base::PersistentHistogramAllocator> histogram_allocator =
       base::GlobalHistogramAllocator::ReleaseForTesting();
 
   // Register the file and allow the "checker" task to run.
-  provider()->RegisterSource(metrics_file(),
-                             FileMetricsProvider::SOURCE_HISTOGRAMS_ACTIVE_FILE,
-                             FileMetricsProvider::ASSOCIATE_CURRENT_RUN,
-                             kMetricsName);
+  provider()->RegisterSource(
+      metrics_file(), FileMetricsProvider::SOURCE_HISTOGRAMS_ACTIVE_FILE,
+      FileMetricsProvider::ASSOCIATE_CURRENT_RUN, nullptr);
 
   // Record embedded snapshots via snapshot-manager.
   OnDidCreateMetricsLog();
   RunTasks();
   EXPECT_EQ(2U, GetSnapshotHistogramCount());
   EXPECT_TRUE(base::PathExists(metrics_file()));
 
   // Make sure a second call to the snapshot-recorder doesn't break anything.
   OnDidCreateMetricsLog();
   RunTasks();
@@ skipping 41 matching lines @@
   OnDidCreateMetricsLog();
   RunTasks();
   EXPECT_EQ(0U, GetSnapshotHistogramCount());
   EXPECT_TRUE(base::PathExists(metrics_file()));
   OnDidCreateMetricsLog();
   RunTasks();
   EXPECT_TRUE(base::PathExists(metrics_file()));
 }
 
 }  // namespace metrics