Add support for single sample metrics.

content/browser/renderer_host/one_shot_metric_host.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 "content/browser/renderer_host/one_shot_metric_host.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "mojo/public/cpp/bindings/strong_binding.h"
+
+namespace content {
+
+// static
+void OneShotMetricHost::Create(mojom::OneShotMetricHostRequest request) {
+  LOG(ERROR) << __func__;
+  mojo::MakeStrongBinding(base::MakeUnique<OneShotMetricHost>(),
+                          std::move(request));
+}
+
+OneShotMetricHost::OneShotMetricHost() {
+  LOG(ERROR) << __func__;
+}
+
+OneShotMetricHost::~OneShotMetricHost() {
+  LOG(ERROR) << __func__;
+  if (!sample_)
+    return;
+
+  DCHECK(metric_);
+  base::Histogram::FactoryGet(metric_->name_, metric_->min_, metric_->max_,
+                              metric_->bucket_count,
+                              base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->Add(*sample_);
+}
+
+void OneShotMetricHost::Initialize(const std::string& name,
+                                   base::HistogramBase::Sample min,
+                                   base::HistogramBase::Sample max,
+                                   uint32_t bucket_count) {
+  LOG(ERROR) << __func__;
+  DCHECK(!metric_);
+  metric_.reset(new Metric{name, min, max, bucket_count});
+}
+
+void OneShotMetricHost::SetSample(base::HistogramBase::Sample sample) {
+  DCHECK(metric_);
+  sample_.reset(new base::HistogramBase::Sample{sample});
+}
+
+}  // namespace content