Adding reporting of metrics sampling rate.

chrome/browser/metrics/sampling_metrics_provider.h

+// Copyright 2016 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 CHROME_BROWSER_METRICS_SAMPLING_METRICS_PROVIDER_H_
+#define CHROME_BROWSER_METRICS_SAMPLING_METRICS_PROVIDER_H_
+
+#include "components/metrics/metrics_provider.h"
+
+namespace metrics {
+
+// Provides metrics related to sampling of metrics reporting clients. In
+// particular, the rate at which clients are sampled.
+class SamplingMetricsProvider : public MetricsProvider {
+ public:
+  SamplingMetricsProvider();
+  ~SamplingMetricsProvider() override;
+
+ private:
+  // MetricsProvider:
+  void ProvideStabilityMetrics(
+      SystemProfileProto* system_profile_proto) override;
+
+  DISALLOW_COPY_AND_ASSIGN(SamplingMetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // CHROME_BROWSER_METRICS_SAMPLING_METRICS_PROVIDER_H_