Add UMA Histogram Manager to Cronet.

components/metrics/histogram_encoder.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.
+
+// This file defines an utility function that records any changes in a given
+// histogram for transmission.
+
+#ifndef COMPONENTS_METRICS_HISTOGRAM_ENCODER_H_
+#define COMPONENTS_METRICS_HISTOGRAM_ENCODER_H_
+
+#include <string>
+
+#include "base/basictypes.h"
+#include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
+
+namespace base {
+class HistogramSamples;
+}
+
+namespace metrics {
+
+class ChromeUserMetricsExtension;

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

You have an include for this on line 14. You don't need both. Remove one or the
other.

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

Done.

+
+// Record any changes in a given histogram for transmission.
+extern void RecordHistogramDelta(ChromeUserMetricsExtension* uma_proto,

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

Nit: No need for extern.

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

Done.

+                                 const std::string& histogram_name,
+                                 const base::HistogramSamples& snapshot);
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_HISTOGRAM_ENCODER_H_