Limit parallel download to http GET 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 <algorithm>
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 191 matching lines @@
 void ParallelDownloadJob::CreateRequest(int64_t offset, int64_t length) {
   DCHECK(download_item_);
 
   std::unique_ptr<DownloadWorker> worker =
       base::MakeUnique<DownloadWorker>(this, offset, length);
 
   StoragePartition* storage_partition =
       BrowserContext::GetStoragePartitionForSite(
           download_item_->GetBrowserContext(), download_item_->GetSiteUrl());
 
+  // The parallel requests only use GET method.
   std::unique_ptr<DownloadUrlParameters> download_params(
       new DownloadUrlParameters(download_item_->GetURL(),
                                 storage_partition->GetURLRequestContext()));
   download_params->set_file_path(download_item_->GetFullPath());
   download_params->set_last_modified(download_item_->GetLastModifiedTime());
   download_params->set_etag(download_item_->GetETag());
   download_params->set_offset(offset);
 
   // Setting the length will result in range request to fetch a slice of the
   // file.
   download_params->set_length(length);
 
   // Subsequent range requests don't need the "If-Range" header.
   download_params->set_use_if_range(false);
 
   // Subsequent range requests have the same referrer URL as the original
   // download request.
   download_params->set_referrer(Referrer(download_item_->GetReferrerUrl(),
                                          blink::kWebReferrerPolicyAlways));
   // Send the request.
   worker->SendRequest(std::move(download_params));
   DCHECK(workers_.find(offset) == workers_.end());
   workers_[offset] = std::move(worker);
 }
 
 }  // namespace content