Merge multiple histogram snapshots into single one for reporting.

base/metrics/sample_map.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_map.h"
 
 #include "base/logging.h"
 
 namespace base {
 
@@ skipping 20 matching lines @@
 }
 
 Count SampleMap::TotalCount() const {
   Count count = 0;
   for (const auto& entry : sample_counts_) {
     count += entry.second;
   }
   return count;
 }
 
+void SampleMap::Negate() {
+  for (auto& entry : sample_counts_)

[Alexei Svitkine (slow), 2015/12/04 18:30:11]

Nit: const auto&

[bcwhite, 2015/12/08 17:32:18]

Can't be "const" because it's being changed.

+    entry.second = -entry.second;
+}
+
 scoped_ptr<SampleCountIterator> SampleMap::Iterator() const {
   return scoped_ptr<SampleCountIterator>(new SampleMapIterator(sample_counts_));
 }
 
 bool SampleMap::AddSubtractImpl(SampleCountIterator* iter,
                                 HistogramSamples::Operator op) {
   Sample min;
   Sample max;
   Count count;
   for (; !iter->Done(); iter->Next()) {
@@ skipping 34 matching lines @@
     *count = iter_->second;
 }
 
 void SampleMapIterator::SkipEmptyBuckets() {
   while (!Done() && iter_->second == 0) {
     ++iter_;
   }
 }
 
 }  // namespace base