Adds PriorityQueue and PrioritizedDispatcher.

net/dns/dns_transaction.h

 // Copyright (c) 2011 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 NET_DNS_DNS_TRANSACTION_H_
 #define NET_DNS_DNS_TRANSACTION_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 31 matching lines @@
                  const base::StringPiece& qname,
                  uint16 qtype,
                  const ResultCallback& callback,
                  const BoundNetLog& source_net_log);
   ~DnsTransaction();
 
   const DnsQuery* query() const { return query_.get(); }
 
   const DnsResponse* response() const { return response_.get(); }
 
-  // Starts the resolution process.  Will return ERR_IO_PENDING and will
-  // notify the caller via |delegate|.  Should only be called once.
+  // Starts the resolution process. Will return ERR_IO_PENDING and will notify
+  // the caller via |delegate|, except when failing synchronously. Should only
+  // be called once.
   int Start();
 
  private:
   enum State {
     STATE_CONNECT,
     STATE_CONNECT_COMPLETE,
     STATE_SEND_QUERY,
     STATE_SEND_QUERY_COMPLETE,
     STATE_READ_RESPONSE,
     STATE_READ_RESPONSE_COMPLETE,
     STATE_NONE,
   };
 
+  struct Attempt {
+    scoped_ptr<DnsQuery> query_;
+    scoped_ptr<DnsResponse> response_;
+    scoped_ptr<DatagramClientSocket> socket_;
+  };
+
   int DoLoop(int result);
   void DoCallback(int result);
   void OnIOComplete(int result);
 
   int DoConnect();
   int DoConnectComplete(int result);
   int DoSendQuery();
   int DoSendQueryComplete(int result);
   int DoReadResponse();
   int DoReadResponseComplete(int result);
@@ skipping 18 matching lines @@
   base::OneShotTimer<DnsTransaction> timer_;
 
   BoundNetLog net_log_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsTransaction);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_TRANSACTION_H_