Add the download component and initial setup

components/download/internal/background_download_service_impl.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/download/internal/background_download_service_impl.h"
+
+namespace download {
+
+// static
+BackgroundDownloadService* BackgroundDownloadService::Create(
+    const base::FilePath& storage_dir,
+    const scoped_refptr<base::SequencedTaskRunner>& background_task_runner) {
+  return new BackgroundDownloadServiceImpl();
+}
+
+BackgroundDownloadServiceImpl::BackgroundDownloadServiceImpl() = default;
+BackgroundDownloadServiceImpl::~BackgroundDownloadServiceImpl() = default;
+
+void BackgroundDownloadServiceImpl::StartDownload(
+    const DownloadParams& download_params) {}
+void BackgroundDownloadServiceImpl::PauseDownload(const std::string& guid) {}
+void BackgroundDownloadServiceImpl::ResumeDownload(const std::string& guid) {}
+void BackgroundDownloadServiceImpl::CancelDownload(const std::string& guid) {}
+void BackgroundDownloadServiceImpl::ChangeDownloadCriteria(
+    const std::string& guid,
+    const SchedulingParams& params) {}
+
+}  // namespace download