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

content/browser/download/download_resource_handler.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.
 
 #include "content/browser/download/download_resource_handler.h"
 
 #include <string>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 390 matching lines @@
       case net::HTTP_ACCEPTED:
       case net::HTTP_NON_AUTHORITATIVE_INFORMATION:
       case net::HTTP_RESET_CONTENT:
       case net::HTTP_PARTIAL_CONTENT:
         // Expected successful codes.
         break;
       case net::HTTP_NO_CONTENT:
       case net::HTTP_NOT_FOUND:
         reason = DOWNLOAD_INTERRUPT_REASON_SERVER_BAD_CONTENT;
         break;
-      case net::HTTP_PRECONDITION_FAILED:
-        // Failed our 'If-Unmodified-Since' or 'If-Match'; see
-        // download_manager_impl.cc BeginDownload()
-        reason = DOWNLOAD_INTERRUPT_REASON_SERVER_PRECONDITION;
-        break;
       case net::HTTP_REQUESTED_RANGE_NOT_SATISFIABLE:
         // Retry by downloading from the start automatically:
         // If we haven't received data when we get this error, we won't.
         reason = DOWNLOAD_INTERRUPT_REASON_SERVER_NO_RANGE;
         break;
       case net::HTTP_UNAUTHORIZED:
         // Server didn't authorize this request.
         reason = DOWNLOAD_INTERRUPT_REASON_SERVER_UNAUTHORIZED;
         break;
       case net::HTTP_FORBIDDEN:
@@ skipping 116 matching lines @@
     BrowserThread::PostTask(
         BrowserThread::UI, FROM_HERE,
         base::Bind(&DeleteOnUIThread, base::Passed(&tab_info_)));
   }
 
   UMA_HISTOGRAM_TIMES("SB2.DownloadDuration",
                       base::TimeTicks::Now() - download_start_time_);
 }
 
 }  // namespace content