3 files changed, 6 insertions, 4 deletions
diff --git a/base/metrics/histogram_base.h b/base/metrics/histogram_base.h
index f5448e7..dba4395 100644
--- a/base/metrics/histogram_base.h
+++ b/base/metrics/histogram_base.h
@@ -50,8 +50,8 @@ BASE_EXPORT void DeserializeHistogramAndAddSamples(PickleIterator* iter);
 
 class BASE_EXPORT HistogramBase {
  public:
-  typedef int Sample;  // Used for samples.
-  typedef int Count;   // Used to count samples.
+  typedef int Sample;                   // Used for samples.
+  typedef subtle::Atomic32 Count;     // Used to count samples.
 
   static const Sample kSampleType_MAX;  // INT_MAX
 
diff --git a/base/metrics/histogram_samples.cc b/base/metrics/histogram_samples.cc
index 0e0eeb4..9f3dd6a 100644
--- a/base/metrics/histogram_samples.cc
+++ b/base/metrics/histogram_samples.cc
@@ -113,7 +113,8 @@ void HistogramSamples::IncreaseSum(int64 diff) {
 }
 
 void HistogramSamples::IncreaseRedundantCount(HistogramBase::Count diff) {
-  redundant_count_ += diff;
+  base::subtle::NoBarrier_Store(&redundant_count_,
+      base::subtle::NoBarrier_Load(&redundant_count_) + diff);
 }
 
 SampleCountIterator::~SampleCountIterator() {}
diff --git a/base/metrics/sample_vector.cc b/base/metrics/sample_vector.cc
index fe602ee..89233c7 100644
--- a/base/metrics/sample_vector.cc
+++ b/base/metrics/sample_vector.cc
@@ -24,7 +24,8 @@ SampleVector::~SampleVector() {}
 
 void SampleVector::Accumulate(Sample value, Count count) {
   size_t bucket_index = GetBucketIndex(value);
-  counts_[bucket_index] += count;
+  subtle::NoBarrier_Store(&counts_[bucket_index],
+      subtle::NoBarrier_Load(&counts_[bucket_index]) + count);
   IncreaseSum(count * value);
   IncreaseRedundantCount(count);
 }