Add a new UMA enum to record how many download uses parallel requests

content/browser/download/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/download_job.h"
 
 #include "base/bind_helpers.h"
 #include "content/browser/download/download_file.h"
 #include "content/browser/download/download_item_impl.h"
 #include "content/public/browser/browser_thread.h"
@@ skipping 36 matching lines @@
 
   // download_file_ is owned by download_item_ on the UI thread and is always
   // deleted on the FILE thread after download_file_ is nulled out.
   // So it's safe to use base::Unretained here.
   BrowserThread::PostTask(
       BrowserThread::FILE, FROM_HERE,
       base::Bind(&DownloadFile::AddByteStream, base::Unretained(download_file),
                  base::Passed(&stream_reader), offset, length));
 }
 
+bool DownloadJob::UsesParallelRequests() const {
+  return false;
+}
+
 }  // namespace content