Implement FrameMarking header extension support

webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc

Index: webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 790319a99614ca29bfa0198458ac7df8343afd20..32e2ea4f05d83bfee0852ae263b91ccf7ec658cd 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -50,6 +50,8 @@ RTPExtensionType StringToRtpExtensionType(const std::string& extension) {
     return kRtpExtensionVideoContentType;
   if (extension == RtpExtension::kVideoTimingUri)
     return kRtpExtensionVideoTiming;
+  if (extension == RtpExtension::kFrameMarkingUri)
+    return kRtpExtensionFrameMarking;
   RTC_NOTREACHED() << "Looking up unsupported RTP extension.";
   return kRtpExtensionNone;
 }