Add a delay to send the parallel requests.

content/browser/download/parallel_download_job.cc

 // Copyright 2017 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/download/parallel_download_job.h"
 
 #include "base/memory/ptr_util.h"
 #include "content/browser/download/download_create_info.h"
 #include "content/browser/download/parallel_download_utils.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/storage_partition.h"
 
 namespace content {
 
 ParallelDownloadJob::ParallelDownloadJob(
     DownloadItemImpl* download_item,
     std::unique_ptr<DownloadRequestHandleInterface> request_handle,
     const DownloadCreateInfo& create_info)
     : DownloadJobImpl(download_item, std::move(request_handle)),
       initial_request_offset_(create_info.save_info->offset),
       initial_request_length_(create_info.save_info->length) {}
 
 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) {
   DownloadJobImpl::Cancel(user_cancel);
   for (auto& worker : workers_)
     worker->Cancel();
 }
 
 void ParallelDownloadJob::Pause() {
   DownloadJobImpl::Pause();
@@ skipping 83 matching lines @@
   // Subsequent range requests have the same referrer URL as the original
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),
                                          blink::WebReferrerPolicyAlways));
   // Send the request.
   worker->SendRequest(std::move(download_params));
   workers_.push_back(std::move(worker));
 }
 
 }  // namespace content