Add the download component and initial setup

components/download/public/background_download_service.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_DOWNLOAD_PUBLIC_BACKGROUND_DOWNLOAD_SERVICE_H_
+#define COMPONENTS_DOWNLOAD_PUBLIC_BACKGROUND_DOWNLOAD_SERVICE_H_
+
+#include <string>
+
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "base/memory/ref_counted.h"
+#include "base/sequenced_task_runner.h"
+#include "components/keyed_service/core/keyed_service.h"
+
+namespace download {
+
+struct DownloadParams;
+struct SchedulingParams;
+
+// A service responsible for helping facilitate the scheduling and downloading
+// of file content from the web.  See |DownloadParams| for more details on the
+// types of scheduling that can be achieved and the required input parameters
+// for starting a download.  Note that BackgroundDownloadServices with a valid
+// storage directory will persist the requests across restarts.  This means that
+// any feature requesting a download will have to implement a download::Client
+// interface so this class knows who to contact when a download completes after
+// a process restart.
+class BackgroundDownloadService : public KeyedService {

[Peter Beverloo, 2017/05/02 16:12:21]

Why did you decide to go with BackgroundDownloadService and not DownloadService
per the design document?

[David Trainor- moved to gerrit, 2017/05/03 06:02:58]

Will change to DownloadService once your other CL lands.  Thanks for renaming
that! :)

+ public:
+  // |storage_dir| is a path to where all the local storage will be.  This will
+  // hold the internal database as well as any temporary files on disk.  If this
+  // is an empty path, the service will not persist any information to disk and
+  // will act as an in-memory only service (this means no auto-retries after
+  // restarts, no files written on completion, etc.).
+  // |background_task_runner| will be used for all disk reads and writes.
+  static BackgroundDownloadService* Create(
+      const base::FilePath& storage_dir,
+      const scoped_refptr<base::SequencedTaskRunner>& background_task_runner);
+
+  // Sends the download to the service.  A callback to
+  // |DownloadParams::callback| will be triggered once the download has been
+  // persisted and saved in the service
+  virtual void StartDownload(const DownloadParams& download_params) = 0;
+
+  // Allows any feature to pause or resume downloads at will.  Paused downloads
+  // will not start or stop based on scheduling criteria.  They will be
+  // effectively frozen.
+  virtual void PauseDownload(const std::string& guid) = 0;
+  virtual void ResumeDownload(const std::string& guid) = 0;
+
+  // Cancels a download in this service.  The canceled download will be
+  // interrupted if it is running.
+  virtual void CancelDownload(const std::string& guid) = 0;
+
+  // Changes the current scheduling criteria for a download.  This is useful if
+  // a user action might constrain or loosen the device state during which this
+  // download can run.
+  virtual void ChangeDownloadCriteria(const std::string& guid,
+                                      const SchedulingParams& params) = 0;
+
+ protected:
+  BackgroundDownloadService() = default;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BackgroundDownloadService);
+};
+
+}  // namespace download
+
+#endif  // COMPONENTS_DOWNLOAD_PUBLIC_BACKGROUND_DOWNLOAD_SERVICE_H_