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 faaf4c4f785c9f9cb67171a795e07d05afec0d41..99f41be18c6c9519383115e8e7c7f0bbfaa95b6f 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -42,6 +42,8 @@ RTPExtensionType StringToRtpExtensionType(const std::string& extension) {
     return kRtpExtensionPlayoutDelay;
   if (extension == RtpExtension::kVideoContentTypeUri)
     return kRtpExtensionVideoContentType;
+  if (extension == RtpExtension::kFrameMarkingUri)
+    return kRtpExtensionFrameMarking;
   RTC_NOTREACHED() << "Looking up unsupported RTP extension.";
   return kRtpExtensionNone;
 }