Make changing a record's type an atomic operation.

base/metrics/persistent_histogram_allocator.cc

Index: base/metrics/persistent_histogram_allocator.cc
diff --git a/base/metrics/persistent_histogram_allocator.cc b/base/metrics/persistent_histogram_allocator.cc
index 20f64336016ae7acf269c3faa25ba3e8fc585425..789e969d7a687c2695915712422350a742758dee 100644
--- a/base/metrics/persistent_histogram_allocator.cc
+++ b/base/metrics/persistent_histogram_allocator.cc
@@ -480,7 +480,7 @@ void PersistentHistogramAllocator::FinalizeHistogram(Reference ref,
   // 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(