Glue parallel download job and download file together.

content/public/browser/download_item.h

Index: content/public/browser/download_item.h
diff --git a/content/public/browser/download_item.h b/content/public/browser/download_item.h
index 80e0c63cd53514b922698a4faf3d08964a7cba58..48309b60b1e39503fb01a663c43c69b7500c7a7e 100644
--- a/content/public/browser/download_item.h
+++ b/content/public/browser/download_item.h
@@ -117,6 +117,8 @@ class CONTENT_EXPORT DownloadItem : public base::SupportsUserData {
     int64_t received_bytes;
   };
 
+  using ReceivedSlices = std::vector<DownloadItem::ReceivedSlice>;
+
   ~DownloadItem() override {}
 
   // Observation ---------------------------------------------------------------