Add read support of RtpStreamId/RepairedRtpStreamId header extensions.

webrtc/common_types.h

Index: webrtc/common_types.h
diff --git a/webrtc/common_types.h b/webrtc/common_types.h
index e1a4c77d37adf184bb43b0fd87070d635f54d917..eeb3e771526fa4b0ac4627d5a34fc34772b0684b 100644
--- a/webrtc/common_types.h
+++ b/webrtc/common_types.h
@@ -717,6 +717,14 @@ struct RTPHeaderExtension {
   VideoRotation videoRotation;
 
   PlayoutDelay playout_delay = {-1, -1};
+
+  // For identification of a stream when ssrc is not signaled. See
+  // https://tools.ietf.org/html/draft-ietf-avtext-rid-09
+  // TODO(danilchap): Update url from draft to release version.
+  size_t rid_size = 0;
+  char rid[16];

[pthatcher1, 2017/04/06 21:17:34]

The SDP level uses "rid=", but the header extensions are not actually called
"RIDs".    I think you'd be better off with "rtp_stream_id" and
"repaired_rtp_stream_id" here.  If that's too long, perhaps "stream_id and
"rsid" and "repaired_rsid".  

[danilchap, 2017/04/07 07:07:49]

Since structure type already have 'rtp' in it, I'll go for
stream_id/repaired_stream_id.

+  size_t repair_rid_size = 0;
+  char repair_rid[16];

[pthatcher1, 2017/04/06 21:17:34]

The header extension can be more than 16 chars, even though the WebRTC API only
allows WebRTC clients to be up to 16 chars.    They will usually be 1-2 chars,
I'm guessing.  Why don't we just using a std::string here?

[danilchap, 2017/04/07 07:07:49]

std::string will turn this and all dependent structures (RTPHeader,
WebRtcRTPHeader) from POD.
Which will break in some random places since this structures reset or copied
with memset/memcpy sometimes.

long-term would prefer to use std::string.

 };
 
 struct RTPHeader {