[Cast] Correct serialization of packet sequence number.

media/cast/transport/rtp_sender/rtp_sender.cc

 // Copyright 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.
 
 #include "media/cast/transport/rtp_sender/rtp_sender.h"
 
+#include "base/big_endian.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "media/cast/transport/cast_transport_defines.h"
 #include "media/cast/transport/pacing/paced_sender.h"
 
 namespace media {
 namespace cast {
 namespace transport {
 
 namespace {
@@ skipping 110 matching lines @@
         packets_to_resend.push_back(std::make_pair(packet_key, packet_copy));
       } else if (cancel_rtx_if_not_in_list) {
         transport_->CancelSendingPacket(it->first);
       }
     }
     transport_->ResendPackets(packets_to_resend);
   }
 }
 
 void RtpSender::UpdateSequenceNumber(Packet* packet) {
-  uint16 new_sequence_number = packetizer_->NextSequenceNumber();
-  int index = 2;
-  (*packet)[index] = (static_cast<uint8>(new_sequence_number));
-  (*packet)[index + 1] = (static_cast<uint8>(new_sequence_number >> 8));
+  // TODO(miu): This is an abstraction violation.  This needs to be a part of
+  // the overall packet (de)serialization consolidation.
+  static const int kByteOffsetToSequenceNumber = 2;
+  base::BigEndianWriter big_endian_writer(
+      reinterpret_cast<char*>((&packet->front()) + kByteOffsetToSequenceNumber),
+      sizeof(uint16));
+  big_endian_writer.WriteU16(packetizer_->NextSequenceNumber());
 }
 
 }  // namespace transport
 }  //  namespace cast
 }  // namespace media