Introduce ParallelDownloadJob.

content/browser/download/download_job_factory.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_JOB_FACTORY_H_
+#define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_FACTORY_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "content/browser/download/download_create_info.h"
+
+namespace content {
+
+class DownloadJob;
+class DownloadRequestHandleInterface;
+
+// Factory class to create different kinds of DownloadJob.
+class DownloadJobFactory {
+ public:
+  static std::unique_ptr<DownloadJob> CreateJob(
+      std::unique_ptr<DownloadRequestHandleInterface> req_handle,
+      const DownloadCreateInfo& create_info);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_FACTORY_H_