[net/dns] Don't conflate all unhandled errors into DNS_SERVER_FAILED.

net/dns/dns_transaction.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 "net/dns/dns_transaction.h"
 
 #include <deque>
 #include <string>
 #include <vector>
 
@@ skipping 493 matching lines @@
         default:
           // Server failure.
           DCHECK(result.attempt);
           if (result.attempt != attempts_.back()) {
             // This attempt already timed out. Ignore it.
             return AttemptResult(ERR_IO_PENDING, NULL);
           }
           if (MoreAttemptsAllowed()) {
             result = MakeAttempt();
           } else {
-            return AttemptResult(ERR_DNS_SERVER_FAILED, NULL);
+            return AttemptResult(result.rv, NULL);
           }
           break;
       }
     }
     return result;
   }
 
   void OnTimeout() {
     if (callback_.is_null())
       return;
@@ skipping 54 matching lines @@
 }  // namespace
 
 // static
 scoped_ptr<DnsTransactionFactory> DnsTransactionFactory::CreateFactory(
     DnsSession* session) {
   return scoped_ptr<DnsTransactionFactory>(
       new DnsTransactionFactoryImpl(session));
 }
 
 }  // namespace net