Add UMA Histogram Manager to Cronet.

components/metrics/metrics_log.cc

Index: components/metrics/metrics_log.cc
diff --git a/components/metrics/metrics_log.cc b/components/metrics/metrics_log.cc
index 2ea6f89eab4bdf7bd419d566910725a4fafbf958..fdfe3056c796e3efae1cb99dde94714b51cb7ae8 100644
--- a/components/metrics/metrics_log.cc
+++ b/components/metrics/metrics_log.cc
@@ -23,6 +23,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
 #include "base/time/time.h"
+#include "components/metrics/histogram_encoder.h"
 #include "components/metrics/metrics_hashes.h"
 #include "components/metrics/metrics_pref_names.h"
 #include "components/metrics/metrics_provider.h"
@@ -178,36 +179,7 @@ void MetricsLog::RecordUserAction(const std::string& key) {
 void MetricsLog::RecordHistogramDelta(const std::string& histogram_name,
                                       const base::HistogramSamples& snapshot) {
   DCHECK(!closed_);
-  DCHECK_NE(0, snapshot.TotalCount());
-
-  // We will ignore the MAX_INT/infinite value in the last element of range[].
-
-  HistogramEventProto* histogram_proto = uma_proto_.add_histogram_event();
-  histogram_proto->set_name_hash(Hash(histogram_name));
-  histogram_proto->set_sum(snapshot.sum());
-
-  for (scoped_ptr<SampleCountIterator> it = snapshot.Iterator(); !it->Done();
-       it->Next()) {
-    base::Histogram::Sample min;
-    base::Histogram::Sample max;
-    base::Histogram::Count count;
-    it->Get(&min, &max, &count);
-    HistogramEventProto::Bucket* bucket = histogram_proto->add_bucket();
-    bucket->set_min(min);
-    bucket->set_max(max);
-    bucket->set_count(count);
-  }
-
-  // Omit fields to save space (see rules in histogram_event.proto comments).
-  for (int i = 0; i < histogram_proto->bucket_size(); ++i) {
-    HistogramEventProto::Bucket* bucket = histogram_proto->mutable_bucket(i);
-    if (i + 1 < histogram_proto->bucket_size() &&
-        bucket->max() == histogram_proto->bucket(i + 1).min()) {
-      bucket->clear_max();
-    } else if (bucket->max() == bucket->min() + 1) {
-      bucket->clear_min();
-    }
-  }
+  EncodeHistogramDelta(histogram_name, snapshot, &uma_proto_);
 }
 
 void MetricsLog::RecordStabilityMetrics(