Add flag enabling more packets to be retransmittable.

webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h

 /*
  *  Copyright (c) 2012 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 100 matching lines @@
 
 enum KeyFrameRequestMethod { kKeyFrameReqPliRtcp, kKeyFrameReqFirRtcp };
 
 enum RtpRtcpPacketType { kPacketRtp = 0, kPacketKeepAlive = 1 };
 
 enum RetransmissionMode : uint8_t {
   kRetransmitOff = 0x0,
   kRetransmitFECPackets = 0x1,
   kRetransmitBaseLayer = 0x2,
   kRetransmitHigherLayers = 0x4,
+  kConditionallyRetransmitHigherLayers = 0x8,

[danilchap, 2017/08/29 17:31:19]

can you add some comment what 'conditionally' mean.
(this mode is too unobvious)

[sprang_webrtc, 2017/08/31 15:54:28]

Done.

   kRetransmitAllPackets = 0xFF
 };
 
 enum RtxMode {
   kRtxOff                 = 0x0,
   kRtxRetransmitted       = 0x1,  // Only send retransmissions over RTX.
   kRtxRedundantPayloads   = 0x2   // Preventively send redundant payloads
                                   // instead of padding.
 };
 
@@ skipping 344 matching lines @@
 class TransportSequenceNumberAllocator {
  public:
   TransportSequenceNumberAllocator() {}
   virtual ~TransportSequenceNumberAllocator() {}
 
   virtual uint16_t AllocateSequenceNumber() = 0;
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_DEFINES_H_