Glue parallel download job and download file together.

content/browser/download/download_file.h

Index: content/browser/download/download_file.h
diff --git a/content/browser/download/download_file.h b/content/browser/download/download_file.h
index c155cb216ee8c8385b094ad9d0156afeb67c9119..d19b3c38a9520135041f6d24ce206cb3da52e9c4 100644
--- a/content/browser/download/download_file.h
+++ b/content/browser/download/download_file.h
@@ -51,7 +51,8 @@ class CONTENT_EXPORT DownloadFile {
   // Add a byte stream reader to write into a slice of the file, used for
   // parallel download. Called on the file thread.
   virtual void AddByteStream(std::unique_ptr<ByteStreamReader> stream_reader,
-                             int64_t offset) = 0;
+                             int64_t offset,
+                             int64_t length) = 0;
 
   // Rename the download file to |full_path|.  If that file exists
   // |full_path| will be uniquified by suffixing " (<number>)" to the