Add the download component and initial setup

components/download/public/download_params.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/public/download_params.h"
+
+#include "components/download/public/clients.h"
+
+namespace download {
+
+SchedulingParams::SchedulingParams()
+    : priority(DEFAULT),
+      network_requirements(NONE),
+      battery_requirements(BATTERY_INSENSITIVE) {}
+
+RequestParams::RequestParams() : method("GET") {}
+
+DownloadParams::DownloadParams() : client(INVALID) {}
+
+DownloadParams::~DownloadParams() = default;
+
+}  // namespace download