Use factory to create histograms, and refcounts to track lifetimes

This is CL patch 377028 by Raman Tenneti, with minor changes to
make the try-bots happier.

It is cleanup that better ensures lifetimes of histograms (making it harder
for users to abuse them).  

bug=16495 (repairs leak induced by the first landing)
bug=18840 (should make leaks less possible)
tbr=raman.tenneti
Review URL: http://codereview.chromium.org/462027

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@33933 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 14 insertions, 2 deletions

diff --git a/net/disk_cache/stats_histogram.h b/net/disk_cache/stats_histogram.h
index 8db3bb3..995d486 100644
--- a/net/disk_cache/stats_histogram.h
+++ b/net/disk_cache/stats_histogram.h
@@ -5,6 +5,8 @@
 #ifndef NET_DISK_CACHE_STATS_HISTOGRAM_H_
 #define NET_DISK_CACHE_STATS_HISTOGRAM_H_
 
+#include <string>
+
 #include "base/histogram.h"
 
 namespace disk_cache {
@@ -14,6 +16,10 @@ class Stats;
 // This class provides support for sending the disk cache size stats as a UMA
 // histogram. We'll provide our own storage and management for the data, and a
 // SampleSet with a copy of our data.
+//
+// Class derivation of Histogram "deprecated," and should not be copied, and
+// may eventually go away.
+//
 class StatsHistogram : public Histogram {
  public:
   class StatsSamples : public SampleSet {
@@ -23,10 +29,14 @@ class StatsHistogram : public Histogram {
     }
   };
 
-  explicit StatsHistogram(const char* name)
-      : Histogram(name, 1, 1, 2), init_(false) {}
+  explicit StatsHistogram(const std::string& name, Sample minimum,
+                          Sample maximum, size_t bucket_count)
+      : Histogram(name, minimum, maximum, bucket_count), init_(false) {}
   ~StatsHistogram();
 
+  static scoped_refptr<StatsHistogram>
+      StatsHistogramFactoryGet(const std::string& name);
+
   // We'll be reporting data from the given set of cache stats.
   bool Init(const Stats* stats);
 
@@ -35,6 +45,8 @@ class StatsHistogram : public Histogram {
   virtual void SnapshotSample(SampleSet* sample) const;
 
  private:
+  friend class Histogram;
+
   bool init_;
   static const Stats* stats_;
   DISALLOW_COPY_AND_ASSIGN(StatsHistogram);