Make changing a record's type an atomic operation.

base/metrics/persistent_histogram_allocator.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 "base/metrics/persistent_histogram_allocator.h"
 
 #include <memory>
 
 #include "base/files/important_file_writer.h"
 #include "base/lazy_instance.h"
@@ skipping 462 matching lines @@
 void PersistentHistogramAllocator::FinalizeHistogram(Reference ref,
                                                      bool registered) {
   // If the created persistent histogram was registered then it needs to
   // be marked as "iterable" in order to be found by other processes.
   if (registered)
     memory_allocator_->MakeIterable(ref);
   // If it wasn't registered then a race condition must have caused
   // two to be created. The allocator does not support releasing the
   // acquired memory so just change the type to be empty.
   else
-    memory_allocator_->SetType(ref, 0);
+    memory_allocator_->ChangeType(ref, 0, kTypeIdHistogram);
 }
 
 PersistentSampleMapRecords* PersistentHistogramAllocator::UseSampleMapRecords(
     uint64_t id,
     const void* user) {
   return sparse_histogram_data_manager_.UseSampleMapRecords(id, user);
 }
 
 std::unique_ptr<HistogramBase> PersistentHistogramAllocator::AllocateHistogram(
     HistogramType histogram_type,
@@ skipping 264 matching lines @@
   while (true) {
     std::unique_ptr<HistogramBase> histogram =
         import_iterator_.GetNextWithIgnore(record_to_ignore);
     if (!histogram)
       break;
     StatisticsRecorder::RegisterOrDeleteDuplicate(histogram.release());
   }
 }
 
 }  // namespace base