Add a FlexfecReceiver class.

This class is split in interface/implementation classes, since it
will be referenced from the Call level. Its purpose is to interface
the erasure code decoder with a new class FlexfecReceiveStream
(for received packets), as well as with the main RTP pipeline (for
recovered packets).

BUG=webrtc:5654

Review-Url: https://codereview.webrtc.org/2392663006
Cr-Commit-Position: refs/heads/master@{#14594}

webrtc/modules/rtp_rtcp/source/flexfec_receiver_impl.h

@@ -0,0 +1,60 @@
+/*
+ *  Copyright (c) 2016 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.
+ */
+
+#ifndef WEBRTC_MODULES_RTP_RTCP_SOURCE_FLEXFEC_RECEIVER_IMPL_H_
+#define WEBRTC_MODULES_RTP_RTCP_SOURCE_FLEXFEC_RECEIVER_IMPL_H_
+
+#include <memory>
+
+#include "webrtc/base/basictypes.h"
+#include "webrtc/base/sequenced_task_checker.h"
+#include "webrtc/call.h"
+#include "webrtc/modules/rtp_rtcp/include/flexfec_receiver.h"
+#include "webrtc/modules/rtp_rtcp/source/forward_error_correction.h"
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+
+class FlexfecReceiverImpl : public FlexfecReceiver {
+ public:
+  FlexfecReceiverImpl(uint32_t flexfec_ssrc,
+                      uint32_t protected_media_ssrc,
+                      RecoveredPacketReceiver* callback);
+  ~FlexfecReceiverImpl();
+
+  // Implements FlexfecReceiver.
+  bool AddAndProcessReceivedPacket(const uint8_t* packet, size_t packet_length);
+  FecPacketCounter GetPacketCounter() const;
+
+ private:
+  bool AddReceivedPacket(const uint8_t* packet, size_t packet_length);
+  bool ProcessReceivedPackets();
+
+  // Config.
+  const uint32_t flexfec_ssrc_;
+  const uint32_t protected_media_ssrc_;
+
+  // Erasure code interfacing and callback.
+  std::unique_ptr<ForwardErrorCorrection> erasure_code_;
+  ForwardErrorCorrection::ReceivedPacketList received_packets_;
+  ForwardErrorCorrection::RecoveredPacketList recovered_packets_;
+  RecoveredPacketReceiver* const callback_;
+
+  // Logging and stats.
+  Clock* const clock_;
+  int64_t last_recovered_packet_ms_;
+  FecPacketCounter packet_counter_;
+
+  rtc::SequencedTaskChecker sequence_checker_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_FLEXFEC_RECEIVER_IMPL_H_