Add support for single sample metrics.

components/metrics/single_sample_metrics_provider.h

+// Copyright 2017 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_METRICS_SINGLE_SAMPLE_METRICS_PROVIDER_H_
+#define COMPONENTS_METRICS_SINGLE_SAMPLE_METRICS_PROVIDER_H_
+
+#include "base/macros.h"
+#include "base/metrics/histogram_base.h"
+#include "base/threading/thread_checker.h"
+#include "components/metrics/public/interfaces/single_sample_metrics.mojom.h"
+
+namespace metrics {
+
+class SingleSampleMetricsProvider : public mojom::SingleSampleMetricsProvider {
+ public:
+  static void Create(mojom::SingleSampleMetricsProviderRequest request);
+
+  SingleSampleMetricsProvider();
+  ~SingleSampleMetricsProvider() override;
+
+ private:
+  void AcquireSingleSampleMetric(
+      const std::string& name,
+      base::HistogramBase::Sample min,
+      base::HistogramBase::Sample max,
+      uint32_t bucket_count,
+      int32_t flags,
+      mojom::SingleSampleMetricRequest request) override;
+
+  // Providers must be created, used on, and destroyed on the same thread.
+  base::ThreadChecker thread_checker_;
+
+  DISALLOW_COPY_AND_ASSIGN(SingleSampleMetricsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_SINGLE_SAMPLE_METRICS_PROVIDER_H_