Add support for single sample metrics.

components/metrics/single_value_histograms_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_VALUE_HISTOGRAMS_PROVIDER_H_
+#define COMPONENTS_METRICS_SINGLE_VALUE_HISTOGRAMS_PROVIDER_H_
+
+#include "base/macros.h"
+#include "base/metrics/histogram_base.h"
+#include "components/metrics/public/interfaces/single_value_histograms.mojom.h"
+
+namespace metrics {
+
+class SingleValueHistogramsProvider
+    : public mojom::SingleValueHistogramsProvider {
+ public:
+  static void Create(mojom::SingleValueHistogramsProviderRequest request);
+
+  SingleValueHistogramsProvider();
+  ~SingleValueHistogramsProvider() override;
+
+ private:
+  void AcquireSingleValueCountsHistogram(
+      const std::string& name,
+      base::HistogramBase::Sample min,
+      base::HistogramBase::Sample max,
+      uint32_t bucket_count,
+      mojom::SingleValueCountsHistogramRequest request) override;
+
+  DISALLOW_COPY_AND_ASSIGN(SingleValueHistogramsProvider);
+};
+
+}  // namespace metrics
+
+#endif  // COMPONENTS_METRICS_SINGLE_VALUE_HISTOGRAMS_PROVIDER_H_