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 a6c7647be5e9e3b0d301b450425ecffd7a451dac..371f69aeb82a3d4694d8e3ce88ef1998173ad36a 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;
   if (extension == RtpExtension::kVideoTimingUri)
     return kRtpExtensionVideoTiming;
   RTC_NOTREACHED() << "Looking up unsupported RTP extension.";