Add a helper method to truncate SourceStream's length

content/browser/download/download_item_impl.cc

Index: content/browser/download/download_item_impl.cc
diff --git a/content/browser/download/download_item_impl.cc b/content/browser/download/download_item_impl.cc
index 507ace3f58836cc192837a19cf459b4915197981..04d6f71e97766adb0ad783dc4e4e7b5c86888f6f 100644
--- a/content/browser/download/download_item_impl.cc
+++ b/content/browser/download/download_item_impl.cc
@@ -1980,7 +1980,6 @@ void DownloadItemImpl::ResumeInterruptedDownload(
     std::vector<DownloadItem::ReceivedSlice> slices_to_download
         = FindSlicesToDownload(received_slices_);
     download_params->set_offset(slices_to_download[0].offset);
-    download_params->set_length(slices_to_download[0].received_bytes);
   } else {
     download_params->set_offset(GetReceivedBytes());
   }