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 "base/metrics/histogram_flattener.h"
+#include "base/metrics/histogram_snapshot_manager.h"
+#include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
+
+namespace cronet {
+
+bool HistogramManagerRegisterJni(JNIEnv* env);
+
+// A HistogramManager instance is created by Android.  It is the central
+// controller for the acquisition of log data, and the automatic transmission of
+// that log data to an external server.
+class HistogramManager : public base::HistogramFlattener {
+ public:
+  HistogramManager();
+  ~HistogramManager();
+
+  // ---------------------------
+  // HistogramFlattener methods:

[Alexei Svitkine (slow), 2014/12/10 21:50:17]

Nit: I think convention for new code is to have this comment just be:

// base::HistogramFlattener:

Also, these methods can all be private, I think.

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

Done.

+  // ---------------------------
+  void RecordDelta(const base::HistogramBase& histogram,
+                   const base::HistogramSamples& snapshot) override;
+  void InconsistencyDetected(
+      base::HistogramBase::Inconsistency problem) override;
+  void UniqueInconsistencyDetected(
+      base::HistogramBase::Inconsistency problem) override;
+  void InconsistencyDetectedInLoggedCount(int amount) override;
+
+  // Snapshot all histograms to record the delta by calling
+  // |histogram_snapshot_manager_|'s PrepareDeltas() method.
+  void PrepareDeltas();
+
+  const metrics::ChromeUserMetricsExtension& uma_proto() const {
+    return uma_proto_;
+  }
+
+ private:
+  void RecordHistogramDelta(const std::string& histogram_name,
+                            const base::HistogramSamples& snapshot);
+
+  base::HistogramSnapshotManager histogram_snapshot_manager_;
+
+  // 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_