Add support for single sample metrics.

components/metrics/single_sample_metrics_provider.cc

+// 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.
+
+#include "components/metrics/single_sample_metrics_provider.h"
+
+#include "base/metrics/single_sample_metrics.h"
+#include "mojo/public/cpp/bindings/strong_binding.h"
+
+namespace metrics {
+
+class MojoSingleSampleMetric : public mojom::SingleSampleMetric {
+ public:
+  MojoSingleSampleMetric(const std::string& name,
+                         base::HistogramBase::Sample min,
+                         base::HistogramBase::Sample max,
+                         uint32_t bucket_count,
+                         int32_t flags)
+      : metric_(name, min, max, bucket_count, flags) {}
+  ~MojoSingleSampleMetric() override {}
+
+ private:
+  // mojom::SingleSampleMetric implementation.
+  void SetSample(base::HistogramBase::Sample sample) override {
+    metric_.SetSample(sample);
+  }
+
+  base::DefaultSingleSampleMetric metric_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoSingleSampleMetric);
+};
+
+// static
+void SingleSampleMetricsProvider::Create(
+    mojom::SingleSampleMetricsProviderRequest request) {
+  mojo::MakeStrongBinding(base::MakeUnique<SingleSampleMetricsProvider>(),
+                          std::move(request));
+}
+
+SingleSampleMetricsProvider::SingleSampleMetricsProvider() {}
+
+SingleSampleMetricsProvider::~SingleSampleMetricsProvider() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+}
+
+void SingleSampleMetricsProvider::AcquireSingleSampleMetric(
+    const std::string& name,
+    base::HistogramBase::Sample min,
+    base::HistogramBase::Sample max,
+    uint32_t bucket_count,
+    int32_t flags,
+    mojom::SingleSampleMetricRequest request) {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  mojo::MakeStrongBinding(base::MakeUnique<MojoSingleSampleMetric>(
+                              name, min, max, bucket_count, flags),
+                          std::move(request));
+}
+
+}  // namespace metrics