Add UMA Histogram Manager to Cronet.

components/cronet/android/histogram_manager.h

+// 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.
+
+#ifndef COMPONENTS_CRONET_ANDROID_CRONET_HISTOGRAM_MANAGER_H_
+#define COMPONENTS_CRONET_ANDROID_CRONET_HISTOGRAM_MANAGER_H_
+
+#include <jni.h>
+#include <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
+
+namespace base {
+class HistogramDeltaSerialization;
+class HistogramSamples;
+class HistogramSnapshotManager;
+};

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

Nit: No need for }

+
+namespace cronet {
+
+bool HistogramManagerRegisterJni(JNIEnv* env);
+
+class HistogramManager {
+ public:
+  HistogramManager();
+  ~HistogramManager();
+
+  void UpdateUmaProto();

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

Please add some comments on the methods and on the class (i.e. how the class is
meant to be used).

+
+  std::string SerializeUmaProto();
+
+  const metrics::ChromeUserMetricsExtension& uma_proto() const {
+    return uma_proto_;
+  }
+
+ private:
+  void RecordHistogramDelta(const std::string& histogram_name,
+                            const base::HistogramSamples& snapshot);
+
+  scoped_ptr<base::HistogramDeltaSerialization> histogram_flattener_;
+  scoped_ptr<base::HistogramSnapshotManager> histogram_snapshot_manager_;

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

I don't think this needs to be a scoped_ptr - can just be a member.

+
+  // Stores the protocol buffer representation for this log.
+  metrics::ChromeUserMetricsExtension uma_proto_;
+
+  DISALLOW_COPY_AND_ASSIGN(HistogramManager);
+};
+
+}  // namespace cronet
+
+#endif  // COMPONENTS_CRONET_ANDROID_CRONET_HISTOGRAM_MANAGER_H_