Introduce ParallelDownloadJob.

content/browser/download/download_url_task.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 "content/browser/download/download_url_task.h"
+
+#include "content/browser/download/download_create_info.h"
+#include "content/public/browser/web_contents.h"
+
+namespace content {
+namespace {
+
+const int kVerboseLevel = 1;
+
+std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
+CreateUrlDownloader(std::unique_ptr<DownloadUrlParameters> params,
+                    base::WeakPtr<UrlDownloader::Delegate> delegate) {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
+
+  // Build the URLRequest, BlobDataHandle is hold in original request for image
+  // download.
+  std::unique_ptr<net::URLRequest> url_request =
+      DownloadRequestCore::CreateRequestOnIOThread(DownloadItem::kInvalidId,
+                                                   params.get());
+
+  return std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>(
+      UrlDownloader::BeginDownload(delegate, std::move(url_request),
+                                   params->referrer())
+          .release());
+}
+
+}  // namespace
+
+DownloadUrlTask::DownloadUrlTask() : weak_factory_(this) {}
+
+DownloadUrlTask::~DownloadUrlTask() = default;
+
+void DownloadUrlTask::SendRequest(
+    std::unique_ptr<DownloadUrlParameters> params) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+  BrowserThread::PostTaskAndReplyWithResult(
+      BrowserThread::IO, FROM_HERE,
+      base::Bind(&CreateUrlDownloader, base::Passed(&params),
+                 weak_factory_.GetWeakPtr()),
+      base::Bind(&DownloadUrlTask::AddUrlDownloader,
+                 weak_factory_.GetWeakPtr()));
+}
+
+void DownloadUrlTask::Pause() {
+  request_handle_->PauseRequest();
+}
+
+void DownloadUrlTask::Resume() {
+  request_handle_->ResumeRequest();
+}
+
+void DownloadUrlTask::Cancel() {
+  request_handle_->CancelRequest();
+}
+
+void DownloadUrlTask::OnUrlDownloaderStarted(
+    std::unique_ptr<DownloadCreateInfo> create_info,
+    std::unique_ptr<ByteStreamReader> stream_reader,
+    const DownloadUrlParameters::OnStartedCallback& callback) {
+  // |callback| is not used in subsequent requests.
+  DCHECK(callback.is_null());
+
+  // TODO(xingliu): Pass the |stream_reader| to parallel job and handle failed
+  // request.
+  if (create_info->result !=
+      DownloadInterruptReason::DOWNLOAD_INTERRUPT_REASON_NONE) {
+    VLOG(kVerboseLevel) << "Parallel download sub request failed. reason = "
+                        << create_info->result;
+    NOTIMPLEMENTED();
+    return;
+  }
+
+  request_handle_ = std::move(create_info->request_handle);
+}
+
+void DownloadUrlTask::OnUrlDownloaderStopped(UrlDownloader* downloader) {
+  // Release the |url_downloader_|, the object will be deleted on IO thread.
+  url_downloader_.reset();
+}
+
+void DownloadUrlTask::AddUrlDownloader(
+    std::unique_ptr<UrlDownloader, BrowserThread::DeleteOnIOThread>
+        downloader) {
+  url_downloader_ = std::move(downloader);
+}
+
+}  // namespace content