Use If-Range instead of If-Match/If-Unmodified-Since for partial requests.

content/browser/download/download_item_impl.cc

 // 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.
 
 // File method ordering: Methods in this file are in the same order as
 // in download_item_impl.h, with the following exception: The public
 // interface Start is placed in chronological order with the other
 // (private) routines that together define a DownloadItem's state
 // transitions as the download progresses.  See "Download progression
 // cascade" later in this file.
@@ skipping 873 matching lines @@
       if (force_restart && force_user)
         mode = RESUME_MODE_USER_RESTART;
       else if (force_restart)
         mode = RESUME_MODE_IMMEDIATE_RESTART;
       else if (force_user)
         mode = RESUME_MODE_USER_CONTINUE;
       else
         mode = RESUME_MODE_IMMEDIATE_CONTINUE;
       break;
 
-    case DOWNLOAD_INTERRUPT_REASON_SERVER_PRECONDITION:
     case DOWNLOAD_INTERRUPT_REASON_SERVER_NO_RANGE:
     case DOWNLOAD_INTERRUPT_REASON_FILE_TOO_SHORT:
       if (force_user)
         mode = RESUME_MODE_USER_RESTART;
       else
         mode = RESUME_MODE_IMMEDIATE_RESTART;
       break;
 
     case DOWNLOAD_INTERRUPT_REASON_NETWORK_FAILED:
     case DOWNLOAD_INTERRUPT_REASON_NETWORK_DISCONNECTED:
@@ skipping 900 matching lines @@
     case RESUME_MODE_USER_CONTINUE:
       return "USER_CONTINUE";
     case RESUME_MODE_USER_RESTART:
       return "USER_RESTART";
   }
   NOTREACHED() << "Unknown resume mode " << mode;
   return "unknown";
 }
 
 }  // namespace content