[net/dns] Fix how DnsTransaction computes next server index after fallback.

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 633 matching lines @@
     uint16 id = session_->NextQueryId();
     scoped_ptr<DnsQuery> query;
     if (attempts_.empty()) {
       query.reset(new DnsQuery(id, qnames_.front(), qtype_));
     } else {
       query.reset(attempts_[0]->GetQuery()->CloneWithNewId(id));
     }
 
     const DnsConfig& config = session_->config();
 
-    unsigned server_index = first_server_index_ +
-        (attempt_number % config.nameservers.size());
+    unsigned server_index =
+        (first_server_index_ + attempt_number) % config.nameservers.size();
 
     scoped_ptr<DnsSession::SocketLease> lease =
         session_->AllocateSocket(server_index, net_log_.source());
 
     bool got_socket = !!lease.get();
 
     DnsUDPAttempt* attempt = new DnsUDPAttempt(lease.Pass(), query.Pass());
 
     attempts_.push_back(attempt);
 
@@ skipping 211 matching lines @@
 }  // namespace
 
 // static
 scoped_ptr<DnsTransactionFactory> DnsTransactionFactory::CreateFactory(
     DnsSession* session) {
   return scoped_ptr<DnsTransactionFactory>(
       new DnsTransactionFactoryImpl(session));
 }
 
 }  // namespace net