Introduce ParallelDownloadJob.

content/browser/download/download_item_impl.h

Index: content/browser/download/download_item_impl.h
diff --git a/content/browser/download/download_item_impl.h b/content/browser/download/download_item_impl.h
index c899f25016b113ef24356a9f5cb565b2d8be20e4..b82fa4a4be4e7b04d220ceefacb84c6ceb641857 100644
--- a/content/browser/download/download_item_impl.h
+++ b/content/browser/download/download_item_impl.h
@@ -28,6 +28,7 @@
 namespace content {
 class DownloadFile;
 class DownloadItemImplDelegate;
+class DownloadJob;
 
 // See download_item.h for usage.
 class CONTENT_EXPORT DownloadItemImpl
@@ -228,6 +229,8 @@ class CONTENT_EXPORT DownloadItemImpl
       std::unique_ptr<crypto::SecureHash> hash_state) override;
 
  private:
+  friend class DownloadJob;
+
   // Fine grained states of a download.
   //
   // New downloads can be created in the following states:
@@ -391,6 +394,10 @@ class CONTENT_EXPORT DownloadItemImpl
   // this is.
   void Init(bool active, DownloadType download_type);
 
+  // Initialize download file, this will create the byte stream on file
+  // thread.
+  void InitializeDownloadFile();
+
   // Callback from file thread when we initialize the DownloadFile.
   void OnDownloadFileInitialized(DownloadInterruptReason result);
 
@@ -501,10 +508,6 @@ class CONTENT_EXPORT DownloadItemImpl
   // TODO(rdsmith): Replace with a generalized enum for "download source".
   const bool is_save_package_download_ = false;
 
-  // The handle to the request information.  Used for operations outside the
-  // download system.
-  std::unique_ptr<DownloadRequestHandleInterface> request_handle_;
-
   std::string guid_;
 
   uint32_t download_id_ = kInvalidId;
@@ -677,6 +680,8 @@ class CONTENT_EXPORT DownloadItemImpl
   // Net log to use for this download.
   const net::NetLogWithSource net_log_;
 
+  std::unique_ptr<DownloadJob> job_;
+
   base::WeakPtrFactory<DownloadItemImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DownloadItemImpl);