factor out path id + packet number packing code from the QUIC aead code

net/quic/quic_utils.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.
 //
 // Some helpers for quic.
 
 #ifndef NET_QUIC_QUIC_UTILS_H_
 #define NET_QUIC_QUIC_UTILS_H_
 
 #include <stddef.h>
@@ skipping 96 matching lines @@
 
   // Deletes all the sub-frames contained in |frames|.
   static void DeleteFrames(QuicFrames* frames);
 
   // Deletes all the QuicStreamFrames for the specified |stream_id|.
   static void RemoveFramesForStream(QuicFrames* frames, QuicStreamId stream_id);
 
   // Deletes and clears all the frames and the packet from serialized packet.
   static void ClearSerializedPacket(SerializedPacket* serialized_packet);
 
+  // Returns a packed representation of |path_id| and |packet_number| in which
+  // the highest byte is set to |path_id| and the lower 7 bytes are the lower
+  // 7 bytes of |packet_number|.
+  static uint64_t PackPathIdAndPacketNumber(QuicPathId path_id,
+                                            QuicPacketNumber packet_number);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(QuicUtils);
 };
 
 // Utility function that returns an QuicIOVector object wrapped around |str|.
 // |str|'s data is stored in |iov|.
 inline QuicIOVector MakeIOVector(base::StringPiece str, struct iovec* iov) {
   iov->iov_base = const_cast<char*>(str.data());
   iov->iov_len = static_cast<size_t>(str.size());
   QuicIOVector quic_iov(iov, 1, str.size());
   return quic_iov;
 }
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_UTILS_H_