Add UMA Histogram Manager to Cronet.

components/metrics/histogram_encoder.cc

+// Copyright 2014 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.
+
+#include "components/metrics/histogram_encoder.h"
+
+#include <string>

[Alexei Svitkine (slow), 2014/12/10 15:19:31]

Nit: Add a line after this.

[ramant (doing other things), 2014/12/10 22:27:51]

Done.

+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_samples.h"
+#include "components/metrics/metrics_log.h"

[Alexei Svitkine (slow), 2014/12/10 15:19:31]

This include shouldn't be needed - I think you just need to include the proto
for ChromeUserMetricsExtension.

[ramant (doing other things), 2014/12/10 22:27:51]

This code was calling MetricsLog::Hash. Added a TODO to rename it and move it to
metrics_hashes.h. Will do in the next CL.

+
+using base::SampleCountIterator;
+
+namespace metrics {
+
+// extern

[Alexei Svitkine (slow), 2014/12/10 15:19:31]

Remove comment.

[ramant (doing other things), 2014/12/10 22:27:51]

Done.

+void RecordHistogramDelta(ChromeUserMetricsExtension& uma_proto,

[Alexei Svitkine (slow), 2014/12/10 15:19:31]

Nit: Pass by pointer, also modifiable params should be last.

[ramant (doing other things), 2014/12/10 22:27:51]

Done.

+                          const std::string& histogram_name,
+                          const base::HistogramSamples& snapshot) {
+  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(MetricsLog::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();
+    }
+  }
+}
+
+}  // namespace metrics