Reorganize histograms for persistence.

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 {
 
 typedef HistogramBase::Count Count;
 typedef HistogramBase::Sample Sample;
 
-SampleMap::SampleMap() {}
+SampleMap::SampleMap() : SampleMap(0) {}
+
+SampleMap::SampleMap(uint64_t id) : HistogramSamples(id) {}
 
 SampleMap::~SampleMap() {}
 
 void SampleMap::Accumulate(Sample value, Count count) {
   sample_counts_[value] += count;
   IncreaseSum(count * value);
   IncreaseRedundantCount(count);
 }
 
 Count SampleMap::GetCount(Sample value) const {
@@ skipping 58 matching lines @@
     *count = iter_->second;
 }
 
 void SampleMapIterator::SkipEmptyBuckets() {
   while (!Done() && iter_->second == 0) {
     ++iter_;
   }
 }
 
 }  // namespace base