Re-land https://codereview.chromium.org/23602005: Use nobarrier atomics for lossy counters in base:…

base/metrics/histogram_samples.cc

 // Copyright (c) 2012 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/histogram_samples.h"
 
 #include "base/compiler_specific.h"
 #include "base/pickle.h"
 
 namespace base {
@@ skipping 95 matching lines @@
       return false;
   }
   return true;
 }
 
 void HistogramSamples::IncreaseSum(int64 diff) {
   sum_ += 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() {}
 
 bool SampleCountIterator::GetBucketIndex(size_t* index) const {
   DCHECK(!Done());
   return false;
 }
 
 }  // namespace base