Reorganize histograms for persistence.

base/metrics/histogram_snapshot_manager.h

 // 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.
 
 #ifndef BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 #define BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_
 
 #include <map>
 #include <string>
 
@@ skipping 30 matching lines @@
   // Snapshot this histogram, and record the delta.
   void PrepareDelta(const HistogramBase& histogram);
 
   // Try to detect and fix count inconsistency of logged samples.
   void InspectLoggedSamplesInconsistency(
       const HistogramSamples& new_snapshot,
       HistogramSamples* logged_samples);
 
   // For histograms, track what we've already recorded (as a sample for
   // each histogram) so that we can record only the delta with the next log.
-  std::map<std::string, HistogramSamples*> logged_samples_;
+  std::map<uint64_t, HistogramSamples*> logged_samples_;
 
   // List of histograms found to be corrupt, and their problems.
-  std::map<std::string, int> inconsistencies_;
+  std::map<uint64_t, int> inconsistencies_;
 
   // |histogram_flattener_| handles the logistics of recording the histogram
   // deltas.
   HistogramFlattener* histogram_flattener_;  // Weak.
 
   DISALLOW_COPY_AND_ASSIGN(HistogramSnapshotManager);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_HISTOGRAM_SNAPSHOT_MANAGER_H_