[net/dns] Perform A/AAAA queries for AF_UNSPEC resolutions in parallel.

net/base/prioritized_dispatcher.h

 // 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.
 
 #ifndef NET_BASE_PRIORITIZED_DISPATCHER_H_
 #define NET_BASE_PRIORITIZED_DISPATCHER_H_
 
 #include <vector>
 
 #include "net/base/net_export.h"
@@ skipping 60 matching lines @@
   size_t num_running_jobs() const { return num_running_jobs_; }
   size_t num_queued_jobs() const { return queue_.size(); }
   size_t num_priorities() const { return max_running_jobs_.size(); }
 
   // Adds |job| with |priority| to the dispatcher. If limits permit, |job| is
   // started immediately. Returns handle to the job or null-handle if the job is
   // started. The dispatcher does not own |job|, but |job| must live as long as
   // it is queued in the dispatcher.
   Handle Add(Job* job, Priority priority);
 
+  // Just like Add, except that it adds Job at the font of queue of jobs with
+  // priorities of |priority|.
+  Handle AddAtHead(Job* job, Priority priority);
+
   // Removes the job with |handle| from the queue. Invalidates |handle|.
   // Note: a Handle is valid iff the job is in the queue, i.e. has not Started.
   void Cancel(const Handle& handle);
 
   // Cancels and returns the oldest-lowest-priority Job invalidating any
   // handles to it. Returns NULL if the queue is empty.
   Job* EvictOldestLowest();
 
   // Moves the queued job with |handle| to the end of all values with priority
   // |priority| and returns the updated handle, or null-handle if it starts the
@@ skipping 17 matching lines @@
   std::vector<size_t> max_running_jobs_;
   // Total number of running jobs.
   size_t num_running_jobs_;
 
   DISALLOW_COPY_AND_ASSIGN(PrioritizedDispatcher);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_PRIORITIZED_DISPATCHER_H_