Reorganize histograms for persistence.

base/metrics/statistics_recorder.h

Index: base/metrics/statistics_recorder.h
diff --git a/base/metrics/statistics_recorder.h b/base/metrics/statistics_recorder.h
index 0e5168f4137006080542cc4b15038e4931e387b7..3396829b43de14389839bb6185090656209f5137 100644
--- a/base/metrics/statistics_recorder.h
+++ b/base/metrics/statistics_recorder.h
@@ -28,6 +28,9 @@ class BucketRanges;
 class Lock;
 
 class BASE_EXPORT StatisticsRecorder {
+  // We keep all registered histograms in a map, from name to histogram.
+  typedef std::map<uint64_t, HistogramBase*> HistogramMap;

[Alexei Svitkine (slow), 2015/12/04 18:21:00]

This should be in the private: section below. Also, update the comment please.

[bcwhite, 2015/12/04 19:34:47]

Done.  It actually has to be up top so as to be previously defined when it is
used by something in the "public" section... but that "something" got moved into
the other CL so this will have to migrate over there.

+
  public:
   typedef std::vector<HistogramBase*> Histograms;
 
@@ -95,25 +98,6 @@ class BASE_EXPORT StatisticsRecorder {
   static OnSampleCallback FindCallback(const std::string& histogram_name);
 
  private:
-  // HistogramNameRef holds a weak const ref to the name field of the associated
-  // Histogram object, allowing re-use of the underlying string storage for the
-  // map keys. The wrapper is required as using "const std::string&" as the key
-  // results in compile errors.
-  struct HistogramNameRef {
-    explicit HistogramNameRef(const std::string& name) : name_(name) {};
-
-    // Operator < is necessary to use this type as a std::map key.
-    bool operator<(const HistogramNameRef& other) const {
-      return name_ < other.name_;
-    }
-
-    // Weak, owned by the associated Histogram object.
-    const std::string& name_;
-  };
-
-  // We keep all registered histograms in a map, from name to histogram.
-  typedef std::map<HistogramNameRef, HistogramBase*> HistogramMap;
-
   // We keep a map of callbacks to histograms, so that as histograms are
   // created, we can set the callback properly.
   typedef std::map<std::string, OnSampleCallback> CallbackMap;