Support "shared" histograms between processes.

base/metrics/histogram_samples.cc

Index: base/metrics/histogram_samples.cc
diff --git a/base/metrics/histogram_samples.cc b/base/metrics/histogram_samples.cc
index ec065c602d4df7f780995dc01114032134820ab9..e2fc33dc9a154a0eeeb13d38f762c91be0d1d0dc 100644
--- a/base/metrics/histogram_samples.cc
+++ b/base/metrics/histogram_samples.cc
@@ -87,13 +87,7 @@ void HistogramSamples::SetMetadataId(uint64 id) {
 // that really need it.
 
 void HistogramSamples::Add(const HistogramSamples& other) {
-#ifdef ARCH_CPU_64_BITS
-  subtle::NoBarrier_Store(
-      &meta_->sum,
-      subtle::NoBarrier_Load(&meta_->sum) + other.sum());
-#else  // No Atomic64 on 32-bit platforms.
   meta_->sum += other.sum();
-#endif
 
   HistogramBase::Count old_redundant_count =
       subtle::NoBarrier_Load(&meta_->redundant_count);
@@ -110,13 +104,7 @@ bool HistogramSamples::AddFromPickle(PickleIterator* iter) {
   if (!iter->ReadInt64(&sum) || !iter->ReadInt(&redundant_count))
     return false;
 
-#ifdef ARCH_CPU_64_BITS
-  subtle::NoBarrier_Store(
-      &meta_->sum,
-      subtle::NoBarrier_Load(&meta_->sum) + sum);
-#else  // No Atomic64 on 32-bit platforms.
   meta_->sum += sum;
-#endif
 
   HistogramBase::Count old_redundant_count =
       subtle::NoBarrier_Load(&meta_->redundant_count);
@@ -128,13 +116,7 @@ bool HistogramSamples::AddFromPickle(PickleIterator* iter) {
 }
 
 void HistogramSamples::Subtract(const HistogramSamples& other) {
-#ifdef ARCH_CPU_64_BITS
-  subtle::NoBarrier_Store(
-      &meta_->sum,
-      subtle::NoBarrier_Load(&meta_->sum) - other.sum());
-#else  // No Atomic64 on 32-bit platforms.
   meta_->sum -= other.sum();
-#endif
 
   HistogramBase::Count old_redundant_count =
       subtle::NoBarrier_Load(&meta_->redundant_count);
@@ -145,13 +127,8 @@ void HistogramSamples::Subtract(const HistogramSamples& other) {
 }
 
 bool HistogramSamples::Serialize(Pickle* pickle) const {
-#ifdef ARCH_CPU_64_BITS
-  if (!pickle->WriteInt64(subtle::NoBarrier_Load(&meta_->sum)))
-    return false;
-#else  // No Atomic64 on 32-bit platforms.
   if (!pickle->WriteInt64(meta_->sum))
     return false;
-#endif
   if (!pickle->WriteInt(subtle::NoBarrier_Load(&meta_->redundant_count)))
     return false;
 
@@ -171,13 +148,7 @@ bool HistogramSamples::Serialize(Pickle* pickle) const {
 }
 
 void HistogramSamples::IncreaseSum(int64 diff) {
-#ifdef ARCH_CPU_64_BITS
-  subtle::NoBarrier_Store(
-      &meta_->sum,
-      subtle::NoBarrier_Load(&meta_->sum) + diff);
-#else  // No Atomic64 on 32-bit platforms.
   meta_->sum += diff;
-#endif
 }
 
 void HistogramSamples::IncreaseRedundantCount(HistogramBase::Count diff) {