rtcp::Nack packet moved into own file and got Parse function

webrtc/modules/rtp_rtcp/BUILD.gn

 # 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.
 
 import("../../build/webrtc.gni")
 
@@ skipping 36 matching lines @@
     "source/rtcp_packet.cc",
     "source/rtcp_packet.h",
     "source/rtcp_packet/app.cc",
     "source/rtcp_packet/app.h",
     "source/rtcp_packet/bye.cc",
     "source/rtcp_packet/bye.h",
     "source/rtcp_packet/dlrr.cc",
     "source/rtcp_packet/dlrr.h",
     "source/rtcp_packet/extended_jitter_report.cc",
     "source/rtcp_packet/extended_jitter_report.h",
+    "source/rtcp_packet/nack.cc",
+    "source/rtcp_packet/nack.h",
     "source/rtcp_packet/pli.cc",
     "source/rtcp_packet/pli.h",
     "source/rtcp_packet/psfb.cc",
     "source/rtcp_packet/psfb.h",
     "source/rtcp_packet/receiver_report.cc",
     "source/rtcp_packet/receiver_report.h",
     "source/rtcp_packet/report_block.cc",
     "source/rtcp_packet/report_block.h",
     "source/rtcp_packet/rrtr.cc",
     "source/rtcp_packet/rrtr.h",
+    "source/rtcp_packet/rtpfb.cc",
+    "source/rtcp_packet/rtpfb.h",
     "source/rtcp_packet/transport_feedback.cc",
     "source/rtcp_packet/transport_feedback.h",
     "source/rtcp_packet/voip_metric.cc",
     "source/rtcp_packet/voip_metric.h",
     "source/rtcp_receiver.cc",
     "source/rtcp_receiver.h",
     "source/rtcp_receiver_help.cc",
     "source/rtcp_receiver_help.h",
     "source/rtcp_sender.cc",
     "source/rtcp_sender.h",
@@ skipping 61 matching lines @@
   if (is_win) {
     cflags = [
       # TODO(jschuh): Bug 1348: fix this warning.
       "/wd4267",  # size_t to int truncations
 
       # TODO(kjellander): Bug 261: fix this warning.
       "/wd4373",  # virtual function override.
     ]
   }
 }