Merge multiple histogram snapshots into single one for reporting.

base/metrics/sample_vector.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/sample_vector.h"
 
 #include "base/logging.h"
 #include "base/metrics/bucket_ranges.h"
 
 namespace base {
@@ skipping 48 matching lines @@
 }
 
 Count SampleVector::TotalCount() const {
   Count count = 0;
   for (size_t i = 0; i < counts_size_; i++) {
     count += subtle::NoBarrier_Load(&counts_[i]);
   }
   return count;
 }
 
+void SampleVector::Negate() {
+  for (size_t i = 0; i < counts_size_; i++) {
+    subtle::NoBarrier_Store(&counts_[i],
+                            -subtle::NoBarrier_Load(&counts_[i]));
+  }
+}
+
 Count SampleVector::GetCountAtIndex(size_t bucket_index) const {
   DCHECK(bucket_index < counts_size_);
   return subtle::NoBarrier_Load(&counts_[bucket_index]);
 }
 
 scoped_ptr<SampleCountIterator> SampleVector::Iterator() const {
   return scoped_ptr<SampleCountIterator>(
       new SampleVectorIterator(counts_, counts_size_, bucket_ranges_));
 }
 
@@ skipping 114 matching lines @@
     return;
 
   while (index_ < counts_size_) {
     if (subtle::NoBarrier_Load(&counts_[index_]) != 0)
       return;
     index_++;
   }
 }
 
 }  // namespace base