Add a delay to send the parallel requests.

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 c8bba093fa4d9ed30d7e44329826058fa4f3727c..92981ef56ed2ec22f28e1912dac344fefdd7808a 100644
--- a/content/browser/download/parallel_download_job.cc
+++ b/content/browser/download/parallel_download_job.cc
@@ -25,7 +25,9 @@ ParallelDownloadJob::~ParallelDownloadJob() = default;
 void ParallelDownloadJob::Start() {
   DownloadJobImpl::Start();
 
-  BuildParallelRequests();
+  timer_ = base::MakeUnique<base::OneShotTimer>();
+  timer_->Start(FROM_HERE, GetParallelRequestDelayConfig(), this,
+                &ParallelDownloadJob::BuildParallelRequests);
 }
 
 void ParallelDownloadJob::Cancel(bool user_cancel) {