Add UMA Histogram Manager to Cronet.

components/metrics/histogram_manager.h

Index: components/metrics/histogram_manager.h
diff --git a/components/metrics/histogram_manager.h b/components/metrics/histogram_manager.h
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+// 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 <string>
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/singleton.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 metrics {
+
+// 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();
+
+  // Snapshot all histograms to record the delta into |uma_proto_| and then
+  // returns the serialized protobuf representation of the record.
+  std::vector<uint8> GetDeltas();
+
+  // TODO(mef): Hang Histogram Manager off java object instead of singleton.
+  static HistogramManager* GetInstance();
+
+ private:
+  friend struct DefaultSingletonTraits<HistogramManager>;
+
+  // HistogramFlattener methods:

[Alexei Svitkine (slow), 2014/12/11 20:09:09]

Nit: This comment syntax is preferred instead:

// base::HistogramFlattener:

[ramant (doing other things), 2014/12/11 20:23:53]

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;
+
+  void RecordHistogramDelta(const std::string& histogram_name,

[Alexei Svitkine (slow), 2014/12/11 20:09:09]

This can be removed.

[ramant (doing other things), 2014/12/11 20:23:53]

Done.

+                            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 metrics
+
+#endif  // COMPONENTS_CRONET_ANDROID_CRONET_HISTOGRAM_MANAGER_H_