Add UMA metric to track parallel download requests stats.

content/browser/download/download_create_info.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_
 #define CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 51 matching lines @@
 
   // The size of the response body. If content-length response header is not
   // presented or can't be parse, set to 0.
   int64_t total_bytes;
 
   // The starting position of the initial request.
   // This value matches the offset in DownloadSaveInfo.
   // TODO(xingliu): Refactor to remove |offset| and |length|.
   int64_t offset;
 
-  // The length of the initial request.
-  // This value matches the length in DownloadSaveInfo.
-  int64_t length;
-
   // True if the download was initiated by user action.
   bool has_user_gesture;
 
   base::Optional<ui::PageTransition> transition_type;
 
   // The remote IP address where the download was fetched from.  Copied from
   // UrlRequest::GetSocketAddress().
   std::string remote_address;
 
   // If the download is initially created in an interrupted state (because the
@@ skipping 41 matching lines @@
   // The HTTP connection type.
   net::HttpResponseInfo::ConnectionInfo connection_info;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DownloadCreateInfo);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_DOWNLOAD_DOWNLOAD_CREATE_INFO_H_