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

net/base/priority_queue.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_PRIORITY_QUEUE_H_
 #define NET_BASE_PRIORITY_QUEUE_H_
 
 #include <list>
 #include <vector>
 
@@ skipping 121 matching lines @@
     unsigned id = next_id_;
     valid_ids_.insert(id);
     ++next_id_;
     return Pointer(priority, list.insert(list.end(),
                                          std::make_pair(id, value)));
 #else
     return Pointer(priority, list.insert(list.end(), value));
 #endif
   }
 
+  // Adds |value| with |priority| to the queue. Returns a pointer to the
+  // created element.
+  Pointer InsertAtFront(const T& value, Priority priority) {
+    DCHECK(CalledOnValidThread());
+    DCHECK_LT(priority, lists_.size());
+    ++size_;
+    List& list = lists_[priority];
+#if !defined(NDEBUG)
+    unsigned id = next_id_;
+    valid_ids_.insert(id);
+    ++next_id_;
+    return Pointer(priority, list.insert(list.begin(),
+                                         std::make_pair(id, value)));
+#else
+    return Pointer(priority, list.insert(list.begin(), value));
+#endif
+  }
+
   // Removes the value pointed by |pointer| from the queue. All pointers to this
   // value including |pointer| become invalid.
   void Erase(const Pointer& pointer) {
     DCHECK(CalledOnValidThread());
     DCHECK_LT(pointer.priority_, lists_.size());
     DCHECK_GT(size_, 0u);
 
 #if !defined(NDEBUG)
     DCHECK_EQ(1u, valid_ids_.erase(pointer.id_));
     DCHECK_EQ(pointer.iterator_->first, pointer.id_);
@@ skipping 77 matching lines @@
 
   ListVector lists_;
   size_t size_;
 
   DISALLOW_COPY_AND_ASSIGN(PriorityQueue);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_PRIORITY_QUEUE_H_