Support using UMA_HISTOGRAM_CUSTOM_ENUMERATION from the renderer.

base/metrics/histogram.h

Index: base/metrics/histogram.h
diff --git a/base/metrics/histogram.h b/base/metrics/histogram.h
index e5f0d046725b2547a600e7925f1843c91ce34c25..115c9d830a313b02eb34fc4445bfefc3482956f3 100644
--- a/base/metrics/histogram.h
+++ b/base/metrics/histogram.h
@@ -48,6 +48,7 @@
 
 #include "base/atomicops.h"
 #include "base/base_export.h"
+#include "base/compiler_specific.h"
 #include "base/gtest_prod_util.h"
 #include "base/logging.h"
 #include "base/time.h"
@@ -482,6 +483,7 @@ class BASE_EXPORT Histogram {
   // Pickle class to flatten the object.
   static std::string SerializeHistogramInfo(const Histogram& histogram,
                                             const SampleSet& snapshot);
+
   // The following method accepts a list of pickled histograms and
   // builds a histogram and updates shadow copy of histogram data in the
   // browser process.
@@ -530,6 +532,12 @@ class BASE_EXPORT Histogram {
 
   virtual ~Histogram();
 
+  // Serialize the histogram's ranges to |*pickle|, returning true on success.
+  // Most subclasses can leave this no-op implementation, but some will want to
+  // override it, especially if the ranges cannot be re-derived from other
+  // serialized parameters.
+  virtual bool SerializeRanges(Pickle* pickle) const;
+
   // Initialize ranges_ mapping in cached_ranges_.
   void InitializeBucketRange();
 
@@ -739,10 +747,18 @@ class BASE_EXPORT CustomHistogram : public Histogram {
   static std::vector<Sample> ArrayToCustomRanges(const Sample* values,
                                                  size_t num_values);
 
+  // Helper for deserializing CustomHistograms.  |*ranges| should already be
+  // correctly sized before this call.  Return true on success.
+  static bool DeserializeRanges(void** iter, const Pickle& pickle,
+                                std::vector<Histogram::Sample>* ranges);
+
+
  protected:
   CustomHistogram(const std::string& name,
                   const std::vector<Sample>& custom_ranges);
 
+  virtual bool SerializeRanges(Pickle* pickle) const OVERRIDE;
+
   // Initialize ranges_ mapping in cached_ranges_.
   void InitializedCustomBucketRange(const std::vector<Sample>& custom_ranges);
   virtual double GetBucketSize(Count current, size_t i) const;