Implement Ukm Mojo interface.

components/ukm/public/mojo_ukm_recorder.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_UKM_PUBLIC_MOJO_UKM_RECORDER_H_
+#define COMPONENTS_UKM_PUBLIC_MOJO_UKM_RECORDER_H_
+
+#include "components/ukm/public/interfaces/ukm_interface.mojom.h"
+#include "components/ukm/public/ukm_recorder.h"
+
+namespace ukm {
+
+/**
+ * A helper wrapper that lets UKM data be recorded on other processes with the
+ * same interface that is used in the browser process.
+ *
+ * Usage Example:
+ *
+ *  ukm::mojom::UkmRecorderInterfacePtr interface;
+ *  content::RenderThread::Get()->GetConnector()->BindInterface(
+ *      content::mojom::kBrowserServiceName, mojo::MakeRequest(&interface));
+ *  ukm::MojoUkmRecorder recorder(std::move(interface));
+ *  std::unique_ptr<ukm::UkmEntryBuilder> builder =
+ *      recorder.GetEntryBuilder(coordination_unit_id, "MyEvent");
+ *  builder->AddMetric("MyMetric", metric_value);
+ */
+class MojoUkmRecorder : public UkmRecorder {
+ public:
+  MojoUkmRecorder(mojom::UkmRecorderInterfacePtr interface);
+  ~MojoUkmRecorder() override;
+
+ private:
+  // UkmRecorder:
+  void UpdateSourceURL(SourceId source_id, const GURL& url) override;
+  void AddEntry(mojom::UkmEntryPtr entry) override;
+
+  mojom::UkmRecorderInterfacePtr interface_;
+
+  DISALLOW_COPY_AND_ASSIGN(MojoUkmRecorder);
+};
+
+}  // namespace ukm
+
+#endif  // COMPONENTS_UKM_PUBLIC_MOJO_UKM_RECORDER_H_