Add control to use If-Range header for range request.

content/browser/download/parallel_download_job.cc

Index: content/browser/download/parallel_download_job.cc
diff --git a/content/browser/download/parallel_download_job.cc b/content/browser/download/parallel_download_job.cc
index 2ba903e62670efcf061dac0a4ccde7ea622a6d59..12fe15d1289fbcd10e1b4f4989aada03324ae308 100644
--- a/content/browser/download/parallel_download_job.cc
+++ b/content/browser/download/parallel_download_job.cc
@@ -188,6 +188,9 @@ void ParallelDownloadJob::CreateRequest(int64_t offset, int64_t length) {
   // file.
   download_params->set_length(length);
 
+  // Subsequent range requests don't need the "If-Range" header.
+  download_params->set_use_if_range(false);

[qinmin, 2017/03/30 05:21:43]

still need this?

[xingliu, 2017/03/30 17:16:46]

Yes, I think so.

Precondition failed for initial request and subsequent requests are different.
The initial request will handle the full content returned with http 200 but
subsequent requests need to drop it.

We previously distinguish initial request and subsequent requests based on their
length cap. But subsequent requests now can also be half opened.

Another option is to check the length difference in worker layer, which is not
ideal according to previous review. I guess the main reason is we'd better use
http protocol instead of relying on length checking in worker layer.

+
   // Subsequent range requests have the same referrer URL as the original
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),