Re-add the QUIC DCHECK to ensure packets are always sent in the order of

net/base/linked_hash_map.h

 // Copyright (c) 2013 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.
 //
 // This is a simplistic insertion-ordered map.  It behaves similarly to an STL
 // map, but only implements a small subset of the map's methods.  Internally, we
 // just keep a map and a list going in parallel.
 //
 // This class provides no thread safety guarantees, beyond what you would
 // normally see with std::list.
@@ skipping 61 matching lines @@
   }
 
   // Returns an iterator beyond the first element.
   reverse_iterator rend() {
     return list_.rend();
   }
   const_reverse_iterator rend() const {
     return list_.rend();
   }
 
+  // Front and back accessors common to many stl containers.
+
+  // Returns the earliest-inserted element
+  const value_type& front() const {

[ramant (doing other things), 2014/08/15 01:51:33]

We are only using back(), added front() to be consistent. Hope that is ok.

+    return list_.front();
+  }
+
+  // Returns the earliest-inserted element.
+  value_type& front() {
+    return list_.front();
+  }
+
+  // Returns the most-recently-inserted element.
+  const value_type& back() const {
+    return list_.back();
+  }
+
+  // Returns the most-recently-inserted element.
+  value_type& back() {
+    return list_.back();
+  }
+
   // Clears the map of all values.
   void clear() {
     map_.clear();
     list_.clear();
   }
 
   // Returns true iff the map is empty.
   bool empty() const {
     return list_.empty();
   }
@@ skipping 109 matching lines @@
 
  private:
   // The map component, used for speedy lookups
   MapType map_;
 
   // The list component, used for maintaining insertion order
   ListType list_;
 };
 
 #endif  // UTIL_GTL_LINKED_HASH_MAP_H_