Introduce ParallelDownloadJob.

content/browser/download/download_url_task.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 CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_URL_TASK_H_
+#define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_URL_TASK_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "content/browser/byte_stream.h"
+#include "content/browser/download/download_request_handle.h"
+#include "content/browser/download/url_downloader.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/download_interrupt_reasons.h"
+#include "content/public/browser/download_url_parameters.h"
+
+namespace content {
+
+// Helper class used to send subsequent range requests to fetch segments of the
+// file after handling response of the original non-range request.
+class DownloadUrlTask : public UrlDownloader::Delegate {

[asanka, 2017/02/16 16:27:39]

This class name is pretty confusing given that we have a DownloadUrlJob /
UrlDownloader / DownloadUrlTask/ etc..

[xingliu, 2017/02/20 18:59:11]

Renamed to DownloadWorker in this patch.

+ public:
+  DownloadUrlTask();
+  virtual ~DownloadUrlTask();
+
+  // Send network request to ask for a download.
+  void SendRequest(std::unique_ptr<DownloadUrlParameters> params);
+
+  // Download operations.
+  void Pause();
+  void Resume();
+  void Cancel();
+
+ private:
+  // UrlDownloader::Delegate implementation.
+  void OnUrlDownloaderStarted(
+      std::unique_ptr<DownloadCreateInfo> create_info,
+      std::unique_ptr<ByteStreamReader> stream_reader,
+      const DownloadUrlParameters::OnStartedCallback& callback) override;
+  void OnUrlDownloaderStopped(UrlDownloader* downloader) override;
+
+  void AddUrlDownloader(
+      std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
+          downloader);
+
+  // Used to control the network request. Live on UI thread.
+  std::unique_ptr<DownloadRequestHandleInterface> request_handle_;
+
+  // Used to handle the url request. Live and die on IO thread.
+  std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
+      url_downloader_;
+
+  base::WeakPtrFactory<DownloadUrlTask> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DownloadUrlTask);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_URL_TASK_H_