Glue parallel download job and download file together.

content/browser/download/download_job.h

Index: content/browser/download/download_job.h
diff --git a/content/browser/download/download_job.h b/content/browser/download/download_job.h
index 836cfdaa36679789b58188b2cded13af1f9c8d00..532447a9e7cf9119ce9690c4ee061593f95ced3b 100644
--- a/content/browser/download/download_job.h
+++ b/content/browser/download/download_job.h
@@ -7,6 +7,7 @@
 
 #include "base/macros.h"
 #include "base/time/time.h"
+#include "content/browser/byte_stream.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/download_danger_type.h"
 #include "content/public/browser/download_interrupt_reasons.h"
@@ -42,6 +43,11 @@ class CONTENT_EXPORT DownloadJob {
  protected:
   void StartDownload() const;
 
+  // Add a byte stream to the download sink.
+  void AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
+                     int64_t offset,
+                     int64_t length);
+
   DownloadItemImpl* download_item_;
 
  private: