Adding reporting of metrics sampling rate.

chrome/browser/metrics/sampling_metrics_provider.cc

+// 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.
+
+#include "chrome/browser/metrics/sampling_metrics_provider.h"
+
+#include "base/metrics/sparse_histogram.h"
+#include "chrome/browser/metrics/chrome_metrics_services_manager_client.h"
+#include "components/metrics/metrics_provider.h"
+
+namespace metrics {
+
+SamplingMetricsProvider::SamplingMetricsProvider() {}
+SamplingMetricsProvider::~SamplingMetricsProvider() {}
+
+void SamplingMetricsProvider::ProvideStabilityMetrics(
+    SystemProfileProto* system_profile_proto) {
+  int sample_rate;
+  // Only log the sample rate if it's defined.
+  if (ChromeMetricsServicesManagerClient::GetSamplingRatePerMille(
+          &sample_rate)) {
+    base::HistogramBase* histogram = base::SparseHistogram::FactoryGet(
+        "UMA.SamplingRatePerMille",
+        base::HistogramBase::kUmaStabilityHistogramFlag);
+    histogram->Add(sample_rate);
+  }
+}
+
+}  // namespace metrics