Add a FlexfecReceiver class.

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")
 
 rtc_static_library("rtp_rtcp") {
   sources = [
     "include/fec_receiver.h",
+    "include/flexfec_receiver.h",
     "include/receive_statistics.h",
     "include/remote_ntp_time_estimator.h",
     "include/rtp_header_parser.h",
     "include/rtp_payload_registry.h",
     "include/rtp_receiver.h",
     "include/rtp_rtcp.h",
     "include/rtp_rtcp_defines.h",
     "mocks/mock_rtp_rtcp.h",
     "source/byte_io.h",
     "source/dtmf_queue.cc",
     "source/dtmf_queue.h",
     "source/fec_private_tables_bursty.h",
     "source/fec_private_tables_random.h",
     "source/fec_receiver_impl.cc",
     "source/fec_receiver_impl.h",
     "source/flexfec_header_reader_writer.cc",
     "source/flexfec_header_reader_writer.h",
+    "source/flexfec_receiver_impl.cc",
+    "source/flexfec_receiver_impl.h",
     "source/forward_error_correction.cc",
     "source/forward_error_correction.h",
     "source/forward_error_correction_internal.cc",
     "source/forward_error_correction_internal.h",
     "source/mock/mock_rtp_payload_strategy.h",
     "source/packet_loss_stats.cc",
     "source/packet_loss_stats.h",
     "source/playout_delay_oracle.cc",
     "source/playout_delay_oracle.h",
     "source/producer_fec.cc",
@@ skipping 154 matching lines @@
       "test/testFec/test_packet_masks_metrics.cc",
     ]
 
     deps = [
       ":rtp_rtcp",
       "//testing/gtest",
       "//webrtc/test:test_support_main",
     ]
   }  # test_packet_masks_metrics
 }