Add UMA Histogram Manager to Cronet.

components/cronet/android/histogram_manager.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/cronet/android/histogram_manager.h"
+
+#include <string>
+
+#include "base/android/jni_array.h"
+#include "base/metrics/histogram_delta_serialization.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/metrics/histogram_snapshot_manager.h"
+#include "base/metrics/sample_map.h"
+#include "base/metrics/statistics_recorder.h"
+#include "components/metrics/metrics_hashes.h"
+#include "components/metrics/metrics_log.h"
+#include "components/metrics/proto/histogram_event.pb.h"
+
+#include "jni/HistogramManager_jni.h"
+
+using base::SampleCountIterator;
+
+namespace cronet {
+
+static const char kCronetHistogramName[] = "cronet";
+
+// Explicitly register static JNI functions.
+bool HistogramManagerRegisterJni(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+HistogramManager::HistogramManager() {
+  histogram_flattener_.reset(
+      new base::HistogramDeltaSerialization(kCronetHistogramName));
+  histogram_snapshot_manager_.reset(
+      new base::HistogramSnapshotManager(histogram_flattener_.get()));

[Alexei Svitkine (slow), 2014/12/03 16:46:53]

Instead of creating a flattener,  HistogramManager should just implement
base::HistogramFlattener.

Then, RecordDelta() will be called on HistogramManager, which can then call
RecordHistogramDelta() from that method, passing histogram.histogram_name() as
the first param.

+}
+
+HistogramManager::~HistogramManager() {
+}
+
+void HistogramManager::RecordHistogramDelta(const std::string& histogram_name,

[Alexei Svitkine (slow), 2014/12/03 16:46:53]

I think we should avoid duplicating this code - so that we make sure to keep the
code in sync as it evolves.

Here's my suggestion:

Create a new file in components/metrics:

histogram_encoder.cc

We can then define this as a stand-alone method in there that takes uma_proto as
an additional param as a pointer.

Then, both this file and metrics_log.cc can call that version of the code.

+    const base::HistogramSamples& snapshot) {
+  // TODO(mef): figure out where should snapshot come from so it isn't empty.
+  DCHECK_NE(0, snapshot.TotalCount());
+  // We will ignore the MAX_INT/infinite value in the last element of range[].
+
+  metrics::HistogramEventProto* histogram_proto =
+      uma_proto_.add_histogram_event();
+  histogram_proto->set_name_hash(metrics::HashMetricName(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);
+    metrics::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) {
+    metrics::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();
+    }
+  }
+}
+
+void HistogramManager::UpdateUmaProto() {
+  histogram_snapshot_manager_->PrepareDeltas(
+      base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
+
+  scoped_ptr<base::HistogramSamples> snapshot(new base::SampleMap());
+  RecordHistogramDelta(kCronetHistogramName, *snapshot.get());

[Alexei Svitkine (slow), 2014/12/03 16:46:53]

You shouldn't need to call this manually. Instead, PrepareDeltas() will call
back to its flattener - which per my comment above this class should implement
and call RecordHistogramDeltas from its RecordDelta method.

+}
+
+static jbyteArray GetHistogramDeltas(JNIEnv* env, jobject jcaller) {
+  // TODO(mef): make it singleton?
+  scoped_ptr<HistogramManager> histogram_manager(new HistogramManager());

[Alexei Svitkine (slow), 2014/12/03 16:46:53]

This isn't right. We need to get the deltas only since the last call - which
means that HistogramManager object needs to be kept around.

So we can either make it a singleton or I think preferably if it could hang off
of the Java object (e.g. using a long to store the address of the object).

+  histogram_manager->UpdateUmaProto();
+  int data_size = histogram_manager->uma_proto().ByteSize();
+  std::vector<uint8> data(data_size);
+  if (histogram_manager->uma_proto().SerializeToArray(&data[0], data_size)) {
+    return base::android::ToJavaByteArray(env, &data[0], data_size).Release();
+  }
+
+  return NULL;
+}
+
+}  // namespace cronet