Don't create parallel request until download file is initialized

content/browser/download/download_job.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_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_H_
 
 #include "base/macros.h"
+#include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
 #include "content/browser/byte_stream.h"
+#include "content/browser/download/download_file.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/download_danger_type.h"
 #include "content/public/browser/download_interrupt_reasons.h"
 
 namespace content {
 
 class DownloadItemImpl;
 class WebContents;
 
 // DownloadJob lives on UI thread and subclasses implement actual download logic
 // and interact with DownloadItemImpl.
 // The base class is a friend class of DownloadItemImpl.
 class CONTENT_EXPORT DownloadJob {
  public:
   explicit DownloadJob(DownloadItemImpl* download_item);
   virtual ~DownloadJob();
 
   // Download operations.
-  virtual void Start() = 0;
+  // TODO(qinmin): Remove the |callback| and |download_file_| parameter if
+  // DownloadJob owns download file.
+  void Start(DownloadFile* download_file_,
+             const DownloadFile::InitializeCallback& callback,
+             const DownloadItem::ReceivedSlices& received_slices);
   virtual void Cancel(bool user_cancel) = 0;
   virtual void Pause();
   virtual void Resume(bool resume_request);
 
   bool is_paused() const { return is_paused_; }
 
   // Return the WebContents associated with the download. Usually used to
   // associate a browser window for any UI that needs to be displayed to the
   // user.
   // Or return nullptr if the download is not associated with an active
   // WebContents.
   virtual WebContents* GetWebContents() const = 0;
 
   // Returns whether the download is parallelizable. The download may not send
   // parallel requests as it can be disabled through flags.
   virtual bool IsParallelizable() const;
 
   // Cancel a particular request starts from |offset|, while the download is not
   // canceled. Used in parallel download.
   // TODO(xingliu): Remove this function if download job owns download file.
   virtual void CancelRequestWithOffset(int64_t offset);
 
  protected:
-  void StartDownload() const;
+  // Callback from file thread when we initialize the DownloadFile.
+  virtual void OnDownloadFileInitialized(
+      const DownloadFile::InitializeCallback& callback,
+      DownloadInterruptReason result);
 
   // Add a byte stream to the download sink. Return false if we start to
   // destroy download file.
   bool AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
                      int64_t offset,
                      int64_t length);
 
   DownloadItemImpl* download_item_;
 
  private:
   // If the download progress is paused by the user.
   bool is_paused_;
 
+  base::WeakPtrFactory<DownloadJob> weak_ptr_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(DownloadJob);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_JOB_H_