Add a ParseHeader method to RtcpPacket, for parsing common RTCP header.

webrtc/modules/rtp_rtcp/source/rtcp_packet.cc

 /*
  *  Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 725 matching lines @@
 //   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 //  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 //  |V=2|P| RC/FMT  |      PT       |             length            |
 //  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 void RtcpPacket::CreateHeader(
     uint8_t count_or_format,  // Depends on packet type.
     uint8_t packet_type,
     size_t length,
     uint8_t* buffer,
-    size_t* pos) const {
+    size_t* pos) {
   assert(length <= 0xffff);
   const uint8_t kVersion = 2;
   AssignUWord8(buffer, pos, (kVersion << 6) + count_or_format);
   AssignUWord8(buffer, pos, packet_type);
   AssignUWord16(buffer, pos, length);
 }
 
 bool Empty::Create(uint8_t* packet,
                    size_t* index,
                    size_t max_length,
@@ skipping 463 matching lines @@
   return length_;
 }
 
 void RawPacket::SetLength(size_t length) {
   assert(length <= buffer_length_);
   length_ = length;
 }
 
 }  // namespace rtcp
 }  // namespace webrtc