Improved iterator for persistent memory allocator.

components/metrics/file_metrics_provider.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/command_line.h"
 #include "base/files/file.h"
 #include "base/files/file_util.h"
 #include "base/files/memory_mapped_file.h"
@@ skipping 156 matching lines @@
       base::Bind(&FileMetricsProvider::CheckAndMapNewMetricFilesOnTaskRunner,
                  base::Unretained(check_list)),
       base::Bind(&FileMetricsProvider::RecordFilesChecked,
                  weak_factory_.GetWeakPtr(), base::Owned(check_list)));
 }
 
 void FileMetricsProvider::RecordHistogramSnapshotsFromFile(
     base::HistogramSnapshotManager* snapshot_manager,
     FileInfo* file) {
   DCHECK(thread_checker_.CalledOnValidThread());
-  base::PersistentHistogramAllocator::Iterator histogram_iter;
-  file->allocator->CreateIterator(&histogram_iter);
+  base::PersistentHistogramAllocator::Iterator histogram_iter(
+      file->allocator.get());
 
   int histogram_count = 0;
   while (true) {
-    scoped_ptr<base::HistogramBase> histogram =
-        file->allocator->GetNextHistogram(&histogram_iter);
+    scoped_ptr<base::HistogramBase> histogram = histogram_iter.GetNext();
     if (!histogram)
       break;
     if (file->type == FILE_HISTOGRAMS_ATOMIC)
       snapshot_manager->PrepareAbsoluteTakingOwnership(std::move(histogram));
     else
       snapshot_manager->PrepareDeltaTakingOwnership(std::move(histogram));
     ++histogram_count;
   }
 
   DVLOG(1) << "Reported " << histogram_count << " histograms from "
@@ skipping 89 matching lines @@
     if (file->type == FILE_HISTOGRAMS_ATOMIC) {
       DCHECK(!file->mapped);
       file->allocator.reset();
       file->data.clear();
       RecordFileAsSeen(file.get());
     }
   }
 }
 
 }  // namespace metrics